Because dyeing results are the product of so many variables: dilution, type of fabric, temperature, manipulation of fabric, age of dye etc, there is always a bit of serendipity. Plus, if you are constantly experimenting to see if you can get new and interesting patterns, you are sometimes going to get ugly.
It's a shame I can't find a picture of this piece of fabric before I added the blue. But I probably didn't take one because it was such an uninspiring, insipid yellow.
It's a half metre piece, so I folded it in half and then formed some sort of circle shape that I fastened with rubber bands (I can still see the rubber band marks) and over dyed it with navy blue.
Hmmmm. Still pretty uninspiring. The contrast was pretty wild, I couldn't ever see myself finding a use for it in my studio, so I stuffed it back into the 'one day I'll overdye it' bag.
One day I did overdye it. This time with an orange. I think I made it even worse....
Woe is me! I couldn't even bear the thought of putting it on the back of a quilt. So in a last ditch effort, I cut it into two fat quarters. One I dyed black and one I dyed brown:
Well, the brown one still has quite a defined pattern, but the contrast is taken down a peg or two and it almost looks like a wood grain/end of log pattern. I could imagine finding a use for it now.
But the black! The black I call success! There is a subtle richness to it with hints of lots of different colours throughout. You can almost see the original blue pattern but only just. There is nothing flat or dull about this dark colour (you might have to see it up close and personal to really appreciate the fullness of colour - you know what they say about photographs and doing justice and all that).
So. Did you dye an ugly piece of fabric? Well, just keep dyeing it until you get something you like. If all else fails - go black!
(And if even that fails, well, we all need a new clean up rag now and then don't we?)
Edited to add: As my lovely commenters have pointed out, beauty is in the eye of the beholder and what I deem as ugly might be lovely to someone else! So there is another choice if you've dyed an 'ugly' fabric - see if someone else loves it and wants to give it a home...