One of the weakest spots in Windowblinds is text legibility. Here are some suggestions.
1. Provide a feature that Photoshop calls "outer glow". This would put a 1 or 2 pixel border around the text and within the open areas of letters like "B", "D", etc. That would make text readable on any background. This would really free up the designers to make more complex titlebars and buttons, etc.
2. Give the user complete control over text - typeface, font size, color, shadow, outer glow, etc. This would also mean breaking the text areas into finer divisions. For instance, right now, if I change the color of menu text, using the "Advanced" button, it also changes the button text. The reason that the user needs control over the text is because each computer is different and each user's eyes are different. No rigid design can possibly suit everyone.