arg can't remember stuff in illy...

[captain spanky]

i'm sure there was an easy way to do this but imagine you have 50 straight lines, all parallel to each other... how do you change the line colour to blend from one colour to another?

[Godders]

If they are stroke lines then expand the strokes on them all by:

Object/Path/outline stroke

Make sure all are ungrouped and make them all one shape using pathfinder.

You should then be able to apply a gradient to get your desired effect!

I think that's what you mean??