The darker the color, the faster the van will heat up in the sun. It will be more difficult to keep the inside cool. If you travel with a pet, this could become more concerning.
If you change the color and don't want to have a "cheap looking" paint job, it would require having all the door jambs, under the hood, etc painted. A decent paint job might cost $3-5K, including jambs (maybe $2-3K without the jambs painted). Is a 2000 model RT worth this "investment"?