Miss Treated - those are both beautiful! :D
I like Jenell's idea for the first one, with the lighter yellow up in a corner, working thorugh the darker yellows across the diagonal and finishing with the blues. And for the second one, I too would put all the bright oranges in the centre and radiate out. Also, as Gai says, a block here and there which doesn't 'blend' makes the design more interesting. :D
But really there is no 'right' way to do this and you'll get as many opinions as there are ppl looking! The main thing is that YOU have to like it. :D If you're worried about forever tweaking, set yourself a time limit - then tweak away to your hearts content then when you reach that time, start sewing! They're both so beautiful, you really can't go wrong. :D
EDITED to say - I also ask DH what he thinks - he's got a good 'eye' so a second opinion from a 'non-sewer' is a good thing as well. I don't always do what he suggests though. :wink: