there are a lot more settings for the grid color sets than there are for the charts and coming up with good combos is not simple. Plus, each setting can involve not just the background and foreground colors, but things like borders, fonts, alignment, margins, etc. Plus there is inheritance of values, so row highlight may define just the border for example, so the rest of the settings will be inherited from the "Normal" row style, or whatever other styles. And then, some stuff is changed dynamically at run-time.
Basically, it gets far more intricate and we didn't want to deal with coming up with an editor that took all that into consideration. Just the simple merging of alert highlight with the existing color style is causing some problems as you noticed. Multiply that by 20 or so.
I can give you the configuration file allowing you to modify things if you wish, but hope you are handy with hex color codes (same as used in HTML)