I did some googling on tea dying. It says that if i press the fabric with a hot iron after, that will set the dye. So this maybe looks like a great idea, i think i will try some tea dying on some scrap fabrics, and see what i think of it :)
Here are two quilts i just found online, one is tea dyed, the other is not, and i think it looks good, and i think you're right Yvonne, it wouldn't effect my darker colours, i will def try this with some scraps later