Do you mean it will be based on the site CSS? That would mean on the 2006 theme there won't be alternating highlights, since almost every cell is the same color.
EDIT: Also if it's based on alternating post colors, this means it wouldn't work in any theme other than 2010. The only way to make it work would be to hard-code the colors for each theme or maybe have something like:
Line 1 color: post background #1
Line 2 color: post background #1 - (R=0C,G=0C,B=0C)
Some sort of pseudo code above, not sure how it would be in real code. Basically non-even lines colors would be based on Line 1 and the theme you use, but slightly darker.
Also note that eventually a new theme will be added again.