Wishing you the best with your treatments, be praying for you!  We're sequestered inside also here and avoiding going out except to replenish food and supplies. 

Good luck with your tissuing efforts. 

I've never added drops of color to the EzeDope and have no idea whether this has affected the chemical balance of the EzeDope.  How was the EzeDope applied?  How heavy of a coat was applied?  How many coats were applied? 

My personal experience with EzeDope has had best results when applied with a foam brush or airbrush so that several light coats could be applied after each coat has dried.  The foam brush is almost dry so that there are no possibility of runs.  It's a very very light coat.  The heavier the coat the more sagging you will experience and the ability of the tissue to tighten up is hindered by the thickness of the EzeDope. 

You might try using a hair dryer to apply heat to the wing but don't get the dryer too close to the tissue.  This might get the EzeDope to tighten up some.  If this doesn't work, the only option is to strip the tissue and recover the wing.     Sorry you've had this trouble.