Using the room preview
- Type or pick your shortlist. Enter a HEX code for the walls, the trim and doors, and the ceiling. Most paint brands publish an approximate HEX or RGB value on each color's web page, which is good enough here.
- Decide on a feature wall. Tick on to paint the back wall in the feature color, or leave it off to see one color all round.
- Pick a floor close to yours. The floor fills a large part of the view, and a walnut floor pulls a wall color very differently from pale oak.
- Switch the light. The six buttons imitate north and south daylight, morning and evening sun, and the two most common bulb types. The note under the buttons says what that light does to color.
- Read the numbers. Each color gets its LRV (how much light it reflects) and its undertone. The trim line also shows its contrast against the walls.
Copy link saves the whole room, light included, so you can send it to whoever you're deciding with.
Start with what you're not repainting
The usual mistake is choosing the wall first. The floor, kitchen worktops, a stone fireplace, the sofa you're keeping: those fixed things already have undertones, and the paint has to agree with them.
Look at each fixed item next to a sheet of plain white printer paper. Against the white, most "beige" tiles turn out to be pinkish, yellowish or greenish. A wall with the same lean will look intentional; one with the opposite lean makes both look dirty. Warm oak floors sit well with greige and creamy whites. Gray tile and cool stone usually want a gray or white with a blue or green base.
Light changes paint more than anything else
We ran the preview's light settings on a few typical colors and measured how far each one moves from its chip color (ΔE, where about 2 is the smallest difference most people notice):
| Color | North light | Warm bulbs (2700K) |
|---|---|---|
| Soft greige #C9C1B1 | ΔE 7.2, grayer | ΔE 8.6, yellower |
| Pale cool gray #B9BDBF | ΔE 6.9, bluer | ΔE 11.5, turns beige |
| Warm white #F2EFE8 | ΔE 7.8, gray | ΔE 10.7, cream |
| Navy #26354A | ΔE 2.2 | ΔE 4.9 |
| Terracotta #B2603F | ΔE 6.5 | ΔE 4.0 |
Two things stand out. Pale neutrals move the most, which is why a white or light gray that looked perfect in the shop can be a disappointment at home. Deep colors barely move at all; navy changed less under warm bulbs than greige did under daylight.
Practical rules that follow from it:
- North-facing rooms get cool, indirect light all day. Lean a little warmer than you think you need, and avoid grays with a blue base, which go steely.
- South-facing rooms are bright and warm. Cool colors are safe here, and strong warm colors can feel hot by midday.
- East and west rooms change through the day. Check samples at the time you use the room most: a west-facing living room is mostly seen in evening light.
- Rooms used mainly at night are lit by bulbs. With 2700K bulbs, cool grays lose their coolness. Either choose a slightly cooler paint than you want, or fit 3000K to 3500K bulbs.
What LRV tells you
Light Reflectance Value runs from 0 (black, reflects nothing) to 100 (a perfect white). Manufacturers print it on many color cards. The preview estimates it from the HEX code using the same luminance formula that screen contrast checkers use, so it lands close to the published figure for most colors but won't match it exactly.
| LRV | What to expect on a wall |
|---|---|
| 80 and up | Very light. Brightens a dim room; can look stark in strong sun. |
| 60 to 80 | Light. The safe range for most living spaces. |
| 40 to 60 | Mid-tone. Reads clearly as a color; fine in rooms with decent light. |
| 15 to 40 | Deep. Cozy, enveloping; needs good lighting at night. |
| Below 15 | Very dark. Dramatic, best on one wall or in a room used in the evening. |
Paint on four walls usually looks stronger than the chip, because each wall reflects its color onto the others. If a chip sits right at the edge of what you'd like, go one step lighter or one step grayer.
Undertones without the guesswork
The undertone readout comes from the color's hue angle in OKLCH. A color reported as "barely warm" has so little chroma that the room's light will decide how it reads. The warm white in the presets, #F2EFE8, is one of these: cream under bulbs, nearly gray in north light.
"Subtly" means the lean will survive most lighting, and anything without a qualifier is a definite color. Green-leaning neutrals deserve special care. They look fresh next to plants and natural wood, but next to a pink-beige carpet they can look ill.
Trim, doors and ceiling
- Trim contrast. The ratio shown beside the trim color is the same kind of figure the color contrast checker gives for text. Around 1.1:1 gives a soft, low-contrast look where trim almost disappears. Classic white trim on greige walls lands about 1.5 to 1.6:1, and white on navy goes past 10:1, crisp and graphic.
- Ceilings. A ceiling is lit at a grazing angle, so it always looks darker than the walls; the preview shades it for that reason. Plain white is the default. In a room with a low ceiling, a white with the same undertone as the walls looks more natural than a stark one.
- Color drenching, where trim, walls and ceiling share one color, works best with mid-tones and deep shades. Paste the wall color into all three fields to see it.
Feature walls
The wall you face as you walk in usually makes the best feature wall, or the one behind a bed or sofa. Avoid the window wall: it's seen against bright glass, so whatever you put there looks darker and flatter. Pick a feature color with the same undertone as the main walls; the color palette generator can suggest partners.
Before you buy gallons
The preview narrows a shortlist; it can't make the final decision. For the last two or three colors:
- Paint sample boards at least the size of a sheet of A4, with two coats. Small chips mislead.
- Move them around the room: next to the floor, near the window, on the darkest wall.
- Look in the morning, at dusk and with the lights on at night.
- Keep boards away from the current wall color's edges, which distorts how you see them.
Sheen matters too. Matte hides flaws but marks easily; eggshell or satin suits hallways, kitchens and children's rooms; semi-gloss is for trim and doors.
Limits
The room is a simple model. Each light is a fixed tint and brightness, and walls are shaded by their angle to the window; there is no bounce light between surfaces and no texture. Your screen's own color and brightness also change what you see. Use the preview to compare colors with each other under the same conditions, not as a promise of exactly how a can of paint will look.