Melanin levels are genetically determined, but they can also be increased by exposure to the sun or other sources of ultraviolet rays, like tanning beds
There are a lot of schools of thought about how to best accomplish this, as it is the hardest part of blowing rings: Exhale with rapid, clipped breaths
They include, of course, caffeine (Burton et al., 2020), as well as trigonelline (Perez-Miguez et al., 2019), agmatine (Galgano et al., 2012), spermine (Dias et al., 2012), taurine (Albouchi and Murkovic, 2020), lutidine (Tsegay et al., 2019), 1-(2-aminoethyl)pyrrolidine (Tsegay et al., 2019), 1-methylpyridinium (n-MP) (Burton et al., 2020), and 1,1-dimethylpiperidium (dMP) (Wermann et al., 2014)
When using ashtrays, they should be deep and sturdy and be placed on something that is hard to ignite, such as a table