Thanks for the reply. I really should have added a picture to the question, unfortunately I discarded the last few slides of intestine that were most often discolored, both things happen, normally the connective tissue is completely colorless but overall the slide looks discolored, I look at the slide before dehydrating and it looks fine, the slides are not black under the microscope, I have already changed the alcohols but the problem persists.

This is not really one of my best images. I ended up discarding the slides with bad coloring. This shade of blue is from the camera I used to take the picture; the camera temperature is really low, so I wouldn't use a photo like this. In any case, I can see this discoloration with my eye under the microscope too, and I've seen it under several microscopes. The tissue that should be red is almost transparent in some regions; in this case, the connective tissue was stained better than I reported on other slides.