too many components for flame (color temperature (rainbow)) Christmas lights ::
B4:A4:Y4:X4 -- Red:Green:Blue:Red (!!! a color for the Flame effect -- not generated by this circuit . . .)
using switching and level hold the number of chains reduces to one -- it still might be more practical to use AD and DA converters with digital function generators (?EEPROM) , level hold switced output to gain the voltage 2 color effect of your like ... or use 4 differently biased optos or use a fine adjusted PNP NPN chain (cost efficient) , e.c. . . .
the varying color predecessor of the previous -- an alternative sine generator ::
drawing (supposedly) only 125µA from the 5V source