Hi relly,
Below is based on research I was able to do on the net on solar cars. Bottom line, sorry to say this, I couldn't find a project. Maybe other people will have an idea.
Re size and color: these would require building multiple (in the case of size) and at least one (in the case of color). Building even one solar car, however, is difficult. Did you have one in mind?
If you provide "solar car" to answers.com, you'll get back as background a long article (based on the wikipedia entry for "solar car," note: some of the material in the article may be too advanced.)
There are also links for kits and a full project.
Kits:
Among the links are two solar car kits priced at $22 and $40:
http://www.klutz.com/catalog/product/31 ... gn=General
http://scientificsonline.com/product.asp_Q_pn_E_3081059
In my opinion, I'm not sure that building a kit is a good project, and the kits are expensive.
Full project:
This link is more for background, as it is very expensive and required a team of people. The a video of construction a full-sized solar vehicle is at:
http://www.treehugger.com/files/2007/04 ... _video.php
(A warning: the speaker on the video talks very slowly. So you'll need to do everything you can to stay awake! I managed to watch about half of the 15 minute video before I decided to do something else.)