I actually wasn’t able to find something simple in this forum, so am writing this up as an option.
Just got some pants back from the tailor, light gray wool. Wore for the first time, and bam, coffee stain. Probably some sloshing around as I walked with the coffee.
Internet turned up very little actually, and much was complicated. The one thing that did come up was vinegar, either undiluted or diluted 1:1 or 1:2 vinegar to water. I’m not sure about vinegar as it is acidic, though since normal vinegar is only 5% diluted water, perhaps not terrible. Still, not my first choice.
Anyway, I’ve used isopropyl alcohol to dab away a gravy stain from a light colored silk tie. Worked very well (very faint outline of a stain was still present, but I can live with that). Moreover, rubbing alcohol should be unreactive where acidic solutions might not be. Plus, alcohol evaporates faster than water.
Anyway, sorry not to have before after pictures. Four noticeable coffee stains at the foot of the leg. Blot with 91% alcohol (by volume, standard stuff you can buy at drug store), then blot dry; repeat. I probably did this 4-5 times. Could still see a faint brown stain, so decided I should try a 1:2 solution vinegar to warm water. Blotted twice, with dry blot. Looked like it was working. I then reblotted with rubbing alcohol to get out the vinegar. Voila, stain gone.
I would recommend just blotting the area affected, to avoid spreading the stain. Also, blotted without rubbing, though maybe a light rub would be needed for very dark stain.
I’m not promising that this will work, but it seemed to do the trick for me, and was fairly simple. I did this about 2 hours after the spill. I should also probably bring it to the dry cleaner in the near future, but I don’t think there should be any permanent spotting from my “cleaning solutions”.
Hope this helps.