or, if you -really- want to do away with the color specifications, create a new define...
PHP Code:
!define BGGradient "BGGradient 000000 000080"
${BGGradient} ffff00
OutFile "test.exe"
Section
SectionEnd
But given that BGGradient is an installer attribute that you'd only really use once.. I'm wondering if it's worth the bother.