Actually 00 is the darkest, FF is lightest.
But if you want simplicity you can go for 3 digits of hex (eg. #f0f
) instead of the usual 6 (#ff00ff
). Usually the extra colour resolution that 6 digits gives you is more confusing than helpful.
Lets explain the hex stuff more. In decimal (the usual number system we use, with 10 digits (0 to 9) since thats how many fingers we have - convenient eh) you use the digits 0 to 9 and each digit in the number has a value 10 times that of the number to the right of it, so:
15 in decimal = (10 x 1) + (1 x 5) = 15 (in decimal again
Hexadecimal (shortened to hex) gets used in computers because it happens that 2 digits of hex nicely represents numbers from 0 to 255, the same as one byte in binary (convenient because computers tend to split things down into bytes, but it's a lot easier to write, say, 0f than the binary equivalent 00010000) . In hex there are 16 digits (0 to f, where a = 10, b = 11, c = 12, d = 13, e = 14, f = 15 ... you get the picture - they ran out of digits so they started using letters), likewise each digit now represents 16 times the value of the digit to the right of it.
15 in hex = (16 x 1) + (1 x 5) = 21 in decimal.
(while we're at it binary follows the same rules except it's base 2, there are 2 digits, 0 and 1, and each digit represents 2 times the value of the digit to the right of it).
</geek waffle caused by boredom>
So how does that help colours? In the colour codes each pair in the triplet (first pair representing red, second green, third blue) can have a value from 00 (black) to ff/255 (full brightness). It tends to be a lot easier to work out how your colour will come out if you know how the numbering system works.
I'm not exactly certain but I think the colour mixing behaves slightly differently on computer screens to mixing paint colours because computer screens are emissive light sources whereas paint on paper is reflective (also somewhat annoyingly the eye copes better with reflective sources because 99% of what we see is lit this way).