Algorithm to check similarity of colors

Question

I'm looking for an algorithm that compares two RGB colors and generates a value of their similarity (where similarity means "similar with respect to average human perception").

Any ideas?

EDIT:

Since I cannot answer anymore I decided to put my "solution" as an edit to the question.

I decided to go with a (very) small subset of true-color in my app, so that I can handle comparison of colors by my own. I work with about 30 colors and use hard-coded distances between them.

Since it was an iPhone app I worked with objective-C and the implementation is more or less a matrix representing the table below, which shows the distances between the colors.

Answer 1

RGB distance in the euclidean space is not very similar to "average human perception".

You can use YUV color space, it takes into account this factor :

 |  Y' |     |  0.299     0.587    0.114   | | R |
 |  U  |  =  | -0.14713  -0.28886  0.436   | | G |
 |  V  |     |  0.615    -0.51499 -0.10001 | | B |

You can also use the CIE color space for this purpose.

EDIT:

I shall mention that YUV color space is an inexpensive approximation that can be computed via simple formulas. But it is not perceptually uniform. Perceptually uniform means that a change of the same amount in a color value should produce a change of about the same visual importance. If you need a more precise and rigourous metric you must definitely consider CIELAB color space or an another perceptually uniform space (even if there are no simple formulas for conversion).