How to compare two colors for similarity/difference

See Wikipedia's article on Color Difference for the right leads. Basically, you want to compute a distance metric in some multidimensional colorspace.

But RGB is not "perceptually uniform", so your Euclidean RGB distance metric suggested by Vadim will not match the human-perceived distance between colors. For a start, L*a*b* is intended to be a perceptually uniform colorspace, and the deltaE metric is commonly used. But there are more refined colorspaces and more refined deltaE formulas that get closer to matching human perception.

You'll have to learn more about colorspaces and illuminants to do the conversions. But for a quick formula that is better than the Euclidean RGB metric, just do this:

• Assume that your RGB values are in the sRGB colorspace
• Find the sRGB to L*a*b* conversion formulas
• Convert your sRGB colors to L*a*b*
• Compute deltaE between your two L*a*b* values

It's not computationally expensive, it's just some nonlinear formulas and some multiplications and additions.

Just an idea that first came to my mind (sorry if stupid). Three components of colors can be assumed 3D coordinates of points and then you could calculate distance between points.

F.E.

Point1 has R1 G1 B1
Point2 has R2 G2 B2

Distance between colors is

d=sqrt((r2-r1)^2+(g2-g1)^2+(b2-b1)^2)

Percentage is

p=d/sqrt((255)^2+(255)^2+(255)^2)