I don't wish to be disrespectful, but that solution has been posted here a couple of times - please read before you write.
To be fair though for me this isn't about whether I can have colored icons in MY sidebar, it is about the fact that there are changes from Snow Leopard to Lion that are really worrying.
It used to be that an upgrade to OS X was done when the install finished, you didn't have to personalize( better:modifie) it like you have to do with a new version of Linux or Windows.
It used to be that changes in OS X were an improvement not only aesthetical wise but also more functional - (obviously taste varies... so sometimes it was just more functional)
The changes in Lion are less functional - grey icons, removal of the volume fine controlling, a hidden library and so on... Thoses changes are not only annoying, they are worrying because that shows us that Apple now works on design rather than function. If Apple employees forget about the principles of human interface, they are going to destroy all kinds of functions in future versions of OS X.
According to european law I can return things I bought online within two weeks of shipment - I deinstalled Lion within a week, because I asked myself: what kind of improvement is there and justifies it the amount of work I have to put in, in order to get back the functions of Snow Leopard that they removed? I came to the conclusio that I don't want a system where I feel I was the programmer - if I wanted I would get Linux. Could i get my money back?