I have researched and found a few older threads related to this topic but none seem to catch on. I have played around with this for a little while and through trail and error i have come up with a simple and safe way of doing this, in my opinion.
the silicone mix does not stick to your earphones so if you mess up the mold you can always chuck them in the trash and start over.
I found that getting the kits from westone.com takes the guess work out of everything and storage of the premix, since each pack is able to do two large earmolds, but by halfing the pack you are able to do 4 earmolds that are smaller and a little more appealing.
compared to something smaller
i have not tried painting the silicone but if i do i will post pics. here are a couple of links that provide detailed pics of the two earphones i did .
one thing though, the fit and finish is far better than any tips that i have purchased and at a huge fraction of the cost. the comfort level is amazing. once the cold silicone gets to body temp (takes a minute or two) you forget that you have them in..
the earphones im using are the monoprice 8320 which have a port hole near the nozzle and the monoprice 9396. the link for the 9396 shows a more detailed step of how and what i did. the links are below the pics. the 9396 uses a single flanged tip while the 8320 uses a double flange tip.
i hope that this will give more info on DIY earmolds.. but if you take the proper steps it can be a safe experiment. so far i have done about 8 of these with the ones posted above being my finals that i enjoy.