@madhattr-
Hey... Welcome! Glad to see some new interest in the old Amigas. Now, on with the problem...
Four green boxes??? That's rather strange. I wouldn't think that's a good thing, by any means. It's an error mode of the UAE that I haven't seen before. Which ROM set are you trying to use? I'd start off trying to get a minimum system running, then add in the rest, later.
Your first goal should be to get the "Insert Workbench" screen up. This will at least confirm that you have a baseline parameter configured correctly, and that the ROM is intact, and the Amiga emulation is opening a valid screen on Linux. (I haven't tried UAE on Mandrake 9 - I have run Mandrake before, but always used UAE through Windows.) Anyhow, what I'd recommend starting out is to leave most all UAE settings at the defaults, and simply select the ROM set you'd like to try (1.3 or 3.1 would be my recommendations, as these two are the most tested). Maybe pick to have 8mb Z2 RAM, 1MB chip, and nothing more. (Don't try to add more than 9MB in that configuration as your base config for testing - it'll cause problems) Select to run UAE in a window, rather than open it's own screen, as well. This is the most compatible mode for testing, and you can move up to better emulation settings later, after you get a base running.
Anyhow, if you get that running, in 1.3 you'll be greeted by a white screen with a picture of a hand holding a workbench disk, or in 3.1, you'll have a purple screen with an animation of a disk flying into a floppy drive. Once you get to that stage, you can start playing around on your own, and select the .ADF file for your emulation, or come back for more info on how to configure additional RAM, Picasso Graphics, etc.