if you don't start breeding in good dark hamsters you are never going to get darker hamsters, however on looking at you hamsters at Andover the male you had in the show didn't look that pale and neither did one of the females. the other two were a bit on the pale side though. if i were you i would mate the two darker ones if they aren't related.
if the lines don't improve after a few attempts it may be just as good an idea to re-stock as you might put it, and bring in a few new darker hams.
if you want your normals to improve you must
not mate them with dom spots, i made the big mistake of doing this with one of my lines about 4 gens ago and they are only starting to darken up again from that last litter. however one line i have going (casanova-mai-squeak- are all in it in some way) which i have never bred dom spots into and it has stayed a rich mahogany colour, i have some imoani here who is the 9th generation hamster from mai!!! and she had a litter but unfortunately i didn't keep any as i didn't have the space
Alex