My lashes are really thin too and I've had a hard time finding a good mascara that doesn't just clump up when I put it on. I recently bought Maybellines Volume Express...it has the plastic tip instead of the old bristle tip and I love it! It doesn't clump and it's easy to build on. After the first application I let it sit for a few minutes until its completely dry then dust powder over my lashes and apply another coating. It's an easy way to make thin lashes look fuller!
Try Rimmel's eyelash accelerator. Its sooo nice. It works amazing and grows out your lashes too. Orrr, I use Maybelline's Lots of Lashes mascara. Its so cute and has tiny wand to get to all your lashes. I use that like everyday!
Other than that, if it really bothers you, you would have to try some fake ones. You can find one that aren't expensive and not too dramatic.
You can easily make your lashes longer & darker by using normal mascara, without looking like you're wearing mascara. I'd suggest getting one that doesn't flake at all, firstly. Because that'd be an immediate giveaway. Most non-waterproof mascaras I've tried, even more expensive ones, flake. So I'd suggest getting a waterproof product. L'Oreal Double Extend waterproof formula is great stuff. One end is a base that lengthens & thickens. The other side is the mascara. It would also help to get some mascara wands. You can get a bag of them very cheaply online. Or you could go to a MAC store & pick a couple up there for no charge. Just be sure to buy something while you're there to avoid coming off as rude. You also don't want them thinking you just came there to steal their wands They always have mascara wands for applying their products in-store. I always ask for some when I'm there shopping. It's never been a problem. You'll need several, but the great thing is they can be washed with just soap & water & reused many times. It's also good to have a mixture of different shapes & sizes for top & bottom lashes, as well as to get them looking as natural as possible. Wash them after each use as once the mascara dries on them, they'll be hard & crusty & very difficult to use again. You can leave them soaking in soapy water while you're out so they're easy to clean when you get home. I've also found that vegetable oil removes the mascara fast for quick cleaning. Then just rinse them with soapy water & let dry. Rather than using the brush that's built into the mascara itself to apply it, use your wands. Dip a clean wand into the base side first, get a little bit of product on it - wipe off any excess - and apply. Immediately after applying, comb your lashes out with another dry, unused wand, trying to fan them out. That'll leave just enough product on your lashes to thicken & lengthen them without looking caked on. Next, take another dry, unused wand & dip it in the mascara itself. Apply it to your lashes over top of the base. Once again, immediately comb your lashes out with a dry, unused wand, fanning them out, until you're left with more enhanced, natural looking lashes. I do this when I'm wearing very little or no makeup & it always turns out great. You can easily use black mascara & still have your lashes look natural. But I'd avoid using brown. Most peoples lashes are either black or brownish black. So if you want to avoid black mascara, go for a brownish-black shade.