Probably not to late to dye. Assuming your using veg-tan leather and you have not added anything else or burnished the edges.
As a general rule never experiment on a finished piece, so only use a dye / finish that you know works for you. If you are not sure, test it out first on a piece of scrap.
You seem to know this , but to clarify typically most people dye before sewing. If you attach a picture it may give the good people of this forum additional information to assist you with.
I believe I read on this forum once that the difference between a beginner leather worker and an experienced one is that the experienced one knows how to cover up their mistakes. Good Luck.