Colour on a wall is not colour on a screen
This is the honest starting point for any colour visualiser, and the ones that do not say it are selling something.
Render colour shifts with the light, with the direction the wall faces and with whatever is next to it. A colour that reads warm and creamy on a south-facing wall in June reads flat grey on a north-facing wall in January. The same tin, the same house.
So what this tool is genuinely good for is narrowing ten options to two. It will tell you that anthracite is too heavy on your house, or that the difference between two off-whites is not worth arguing about. It will not tell you exactly what you are going to get.
Why the texture scale matters
A fine through-coloured render and a heavier textured one look completely different in the same colour, and that difference only reads if the texture is drawn at the correct size.
Hence the measurement. If the tape will not reach, you can work it out: a standard UK external door is 838mm wide, and a brick course is 75mm including the mortar joint, so counting courses up a wall gets you there.
Why there are no branded colour numbers here
You will notice these colours have plain descriptive names rather than reference numbers from one of the big colour systems. That is deliberate.
The accurate values for those systems are a product their owners sell. Every free chart of them floating around the internet is an approximation of unknown provenance, and those approximations disagree with each other, sometimes visibly.
Putting a reference number under a swatch that is visibly wrong would be worse than putting no number at all, because somebody orders render off it and renders are not repainted cheaply. So these are our own colours, named for what they are. When you get to the point of ordering, your supplier's own sample board is the reference, not any screen.
Dark colours are a technical decision, not only an aesthetic one
Worth knowing before falling for anthracite. Darker renders absorb more heat, which means more thermal movement and more stress in the render itself.
Some manufacturers restrict how dark you may go on particular systems, and the restriction is usually tighter on insulated render, where the substrate moves more and there is less mass behind it to even out temperature swings. Ask the supplier what their limit is before you commit, because it is a real constraint rather than a caution.
Two things to check before the scaffold arrives
Whether you are allowed. Conservation areas, listed buildings and some housing estates carry restrictions on external colour, and occasionally a lease does. That is a much cheaper question to ask now than once the wall is half done.
What the sample looks like outside. Get boards rather than swatches, put them against the actual wall, and look at them in the morning, at midday and at dusk. Also look at them next to your window frames and your roof, because those are the two things the render will be sitting against forever and neither is going to change to suit it.
The photo stays on your device
It is opened in your browser and never uploaded anywhere. That is true of everything on this site and it is worth stating plainly here, because on this particular tool the file you are handing over is a photograph of the front of your house.
Common questions
Why does the tool ask me to measure the wall?
So the render texture is drawn at the right size. A fine through-coloured render and a heavy textured one look completely different at the same colour, and that difference only shows up if the texture is at the correct scale. One measured dimension across the wall fixes it.
Will the colour look the same on my house?
Almost certainly not exactly, and that is not a fault in the tool. Render colour shifts with light, with the direction the wall faces, and with what is next to it. A colour that looks warm on a south wall in June looks grey on a north wall in January. Use this to narrow ten options to two, then get sample boards.
Why are there no RAL or NCS numbers?
Because the accurate values of those systems are a product the owners sell, and every free chart on the internet is an approximation of unknown provenance that disagrees with the other free charts. A swatch labelled with a reference number that is visibly wrong is worse than no number, because somebody orders render off it. These are our own named colours, described for what they are.
Does render colour affect anything other than looks?
Yes. Darker colours absorb more heat, which means more thermal movement in the render and more stress on it, and some manufacturers restrict how dark you can go on certain systems or on insulated render in particular. Ask the supplier what their limit is before falling in love with anthracite.
Should I match my neighbours?
Worth checking whether you have a choice. Conservation areas, listed buildings and some estates carry restrictions on external colour, and a few leases do too. It is a much cheaper question to ask before the scaffold goes up than after.
Is my photo uploaded?
No. It is opened in your browser and never leaves the device. That matters here more than on most tools, because the photo is the front of your house.