Whatever the dye trader will buy them for, usually 10g (or is it 25?) I believe. Or 1g at the merchant. They're definitely not worth trying to sell to other players, I doubt anyone would buy them.
If you are talking about selling them to other players, I personally sell them somewhere between what the trader sells them for and what the trader will give me for them.
Example: Trader sells Blue Dye for 150G ... He will give me 50G for one
I will try to sell it for 100G to another player
Also note that some dyes are worth at least something.
Black
White
Red
Silver
are are usually above 100 gold at the trader. Blue is also popular and usually worth a little bit.
