1) why is the default skin template too bright then (the only thing I changed was the addition of the stripes and rose)?
2) how do I tone it down without it going grey or silver?
Not sure why it's like that, but it has been known since the template was released that it was too light/bright (if you just create a skin from the default template without making any changes, and compare it to one of the default N17 skins in the game, you will easily see how much brighter/lighter the template skin is compared to the default one).
I don't really understand your comment/question about how to tone it down "without it going grey or silver" - it's supposed to be silver/grey. Generally, just try reducing the brightness and saturation settings and maybe try adding a darker grey/silver looking overlay as an extra layer on top that you can play around with opacity on till you get something that looks right to you and roughly close to some of the other N17 skins in game, and you should be fine.
You may also want to play around with darkening the weathering layers - IIRC, there's one in particular in the N17 template that adds a light grey overtone that tends to make things even brighter instead of dirtier/darker unless you tone it down as well (you'll have to experiment a little to find the exact layer I'm talking about, and I've found it's best to create a duplicate layer and make the experimental changes to that new layer, leaving the original layer alone and simply turning it off (hiding it), so if you mess up and don't like the results you can always go back to the undisturbed default layer).
Also, even though you are supposed to test your skin with those new video settings (bloom, HDR etc.), it would probably help to post a screenshot taken under more "normal"/pleasing settings (e.g., bloom and HDR off) - that's the way a lot of people (myself included) seem to actually fly in RoF and most of the screenshots of prior skins are taken that way, so it will be easier for people to compare your skin in that kind of screenshot to the ones they've seen of other skins and get a better idea if the skin is really too bright or if it's just the bloom/HDR settings making your screenshots look that way.