In my opinion, this is bad advice. Typically you're going to want to use some form of Nickle Accetate solution at high temp in order to seal the pores of the anodized surface. Just a water boil can often lead to a finish with a "sticky" feeling. Furthermore, if you are boiling the dye solution, you are in fact "capping" the pores of the anodizing and perhaps making them too small for the dye solution to enter. Dyes with larger particles like black will not take. Red may perhaps. Yellow will. Boiling your dye solution is like shutting off the faucet before your water glass is full and wondering why you didn't reach the brim. This is not a good idea! A sure indication of a poor sealing job would be a sticking feeling. Staining and color bleach will surely happen over time if this is the case. This is typical to a simple "boil to seal" hobbiests' approach.
But what do I know...? lol
Below is a paintball marker I did several years ago. For those of you interested, it was a System X AutoCocker. Yes...I did very
custom and
specialty Type II anodizing. This is far more advanced than your basic run of the mill stuff. Notice that it is not one color but two and in fact is "acid washed". You might say I dabbled in anodizing for a few years...The below picture doesn't show the true depth and richness of the colors. I spent several hours polishing these components before anodizing which resulted in a subperb high gloss finish but made it difficult to photograph. Yes...Prep is the key to anodizing. That and not using boiling dye solutions...