Try putting it in the freezer to harden the sap. Take it out and move the fabric under the sap to get it to crack. Scrape it off carefully with the edge of a credit card or gift card.
Ditto free and scrape!
Maybe Goof Off.
WD-40, let it soak a few minutes, wipe off. When totally removed walsh it as you normally would.
I haven't tried it on a red color personally. You could always test it on hidden seam area first. I was worried it would leave a greasy stain the first time I used it as iI had just read on the little booklet "100 ways to use WD-40" they had attached to the new can I bought that it would remove tar & I got tar stuck to my new pants went I went to the beach (right where it looked like I had a bathroom accident lol). So I decided I had nothing to lose on that pair of pants. To my surprise you could never tell anything had happened after I tried it. Wish I still had that little booklet but that was 35 years ago.
Hi Jane: Denatured alcohol and isopropyl alcohol will safely remove stains from many fabrics. You can use it to remove ink or sap. Don't use on acetate, rayon, wool or silk. To remove stubborn stains, moisten a cotton ball or cotton cloth with a few drops of denatured or isopropyl alcohol and dab the sap until it is removed. Don't use Rubbing Alcohol, it can bleach your fabric or leave a dye stain. Good luck