What's to like about the Flash's costume? It's red. All over. He's got the yellow boots and the wing thingys over his ears, but otherwise he's just all red.
A slight exaggeration, of course, but there really isn't a whole lot going on with Barry Allen's duds. Ah, but that's where the beauty of the design lay! See, when the Flash was running really fast, you'd see after-images of where he just was. And when he was running really, really fast, there'd just be this red blur behind him.
Except for these two yellow stripes -- one wide one where his boots just were, and one narrower one where his belt and wrist bands were0. Occasionally, there'd be an even narrower band coming off his wing tips. And I'll be darned if that wasn't a really cool visual. Because the placement and size of those yellow elements against a red field makes for a fairly pleasing set of proportions...
And, of course, when he was running too fast to see, the Flash's trim had that jagged lightening bolt effect. A streamlined human figure highlighted with abruptly harsh angles. And the chest emblem provided something to break up the monotony of the two colors.
Interestingly, I never liked Professor Zoom's costume, though it was only different in that it switched the placement of the red and yellow. The larger field of yellow somehow seemed more effeminate to me at the time, and the color balance didn't seem to work nearly as well.