HEllo! First, thanks for your help ...
i did it befor that way as well, because i found this expression for a vector in the maya help, but it tried it and maya gave me this answer (to the exact same line you wrote) :
"Error: Attributes must be of float, integer, or boolean types: color" ...
and thats what i don´t get
...the rest i am familiar with from photoshop.
do you have any idea why maya doesn´t accept that line ?