Why are methanol flames less visible than other flames?
Here's a link to a YouTube video showing a dish of methanol burning next to a dish of ethanol.  The methanol flame is more difficult to see.  Methanol was also widely used as a fuel in the auto racing circuit, until fires that resulted from crashes or fuel filling accidents resulted in "invisible fires" that were difficult to see during daylight, resulting in severe burns to crews and drivers ("you can't fight the fire, if you can't see it", this is one reason why it was replaced by ethanol as a fuel for Indy racing).  

Flame color (visibility) is dependent upon the elemental composition of the material being heated and the temperature to which it is heated.  This is because heat will excite electrons in the element(s) to an excited state; when these electrons return to the ground state visible light (flame test) will often be emitted

If we look at the carbon content of methanol and ethanol we find the following weight percents:

methanol - 38% carbon by weight

ethanol - 52% carbon by weight

If we compare the heats of combustion for methanol and ethanol we find:

methanol $\ce{~~}$ -726 kJ/mol (exothermic)

ethanol $\ce{~~}$ -1368 kJ/mol (much more exothermic)

There's just not much carbon there to burn in methanol!  Consequently burning methanol doesn't get that hot and its flame will not be as colored as materials that burn more exothermically and result in higher temperatures.