ROBLOX Color3 objects use the RGB color model.
A "rainbow" is parameterized in terms of hue which is not a component of the RGB color model, and which ROBLOX doesn't directly support.
There are several color models supporting hue -- HSL, HSV/HSB. Here I will describe HSV.
The Hue - Saturation - Value Color Model
Here is the Wikipedia article I am referencing
For a fully saturated (vivid color) rainbow, we use saturation S as 1 and value (brightness) V as 1 as well.
We thus get chroma C as C = S * V.
For a hue measuring between 0 and 360 degrees, we define a scaled-down version
We use the intermediate value X to be the following:
1 | X = C * (1 - math.abs( (Hp % 2) - 1 ) ) |
From here, we have an unfortunately complicated transformation into RGB that models the zigzags in this figure.
1 | local f = math.floor(Hp) + 1 |
3 | local Cp = {1,2,2,3,3,1} |
4 | local Xp = {2,1,3,2,1,3} |
9 | R1, G1, B1 = unpack(color) |
We now add an amount to each to give it its value (brightness)
2 | R,G,B = R1 + m, G1 + m, B1 + m |
I have confirmed that this works!
Altogether here's a function to do it, and a rainbow maker:
01 | function RGBfromHSV(H,S,V) |
04 | X = C * (1 - math.abs( (Hp % 2) - 1 ) ) |
05 | local f = math.floor(Hp) + 1 |
07 | local Cp = {1,2,2,3,3,1} |
08 | local Xp = {2,1,3,2,1,3} |
12 | R1, G1, B1 = unpack(color) |
14 | return R1 + m, G1 + m, B1 + m |
21 | table.insert(rainbow, Color3.new( RGBfromHSV(i,1,1) ) ) |
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