Compare it to an iPhone. IMO the DX isn't "dull," it is close to natural. My other phone is a Fascinate and the colors sure aren't "dull" - they're "vivid," way over-saturated. I realize that (1) that isn't really an answer and (2) YMMV. Based on the way digital cameras come out of the box, I am clearly a minority.
I prefer the Droid X screen over the Fascinate...Droid X is bright and natural, as jnewell said...and I also agree with jnewell that the Fascinate is way over saturated.
That is funny I had a friend look at my Droid X just yesterday and said they loved how clear my screen was compared to there iphone 3GS and Fascinate ... Droid X is far from dull in color and her device brightness was turned up where mine is set at about a quarter.