color calculation problems.

1. if i have a color value , for example 123456, how can i calc. the 3 RGB element values ??

2. i have 2 RGB sets , for example ( r1,g1,b1 ) , ( r2,g2,b2).
I want to blend it together, 50% 50% transparent.

Is the solution ( (r1+r2)/2, (g1+g2)/2, (b1+b2)/2 ) or else ?

THX.

there is a buttload of info on google

such as

http://www.w3.org/TR/2000/CR-SVG-20001102/masking.html

and

http://palms.ee.princeton.edu/plx/su...-blending.html

edit:: in case you think im being a jerk, im not, i just cant remember the formula right now and if i did it would probably be wrong.

thx.