I would say that it has darkened and browned. Not a ton, but I think it has changed. Not nearly as much as that test board that sat in the full sun all day unprotected. It's still definitely a reddish wood, but probably browner than it was when first finished. It depends on the lighting, too. It never looks just brown. Sometimes it looks like a crimson, hardly brownish at all.
I guess you could say the color is "brick red" -- since bricks vary so much.
The finish is pretty yellowed, which complicates things. For reference, the bass is normally in a case, and comes out 2-3 nights a week for about four hours under artificial light. It has had some outdoor day gigs, and some miscellaneous daytime use, but mostly I noodle around on another bass with high action, so that this one always feels good and easy when I take it out.