It is pollens, trace amounts of honey, and resins(propolis) that cause the yellow and other colors of wax. Wax that is white/pale has less.
The dark grains on the bottom of the wax chunks are bits of bees, dust, propolis, and other.
In simplest format, wax rendering and end use is a 4 stage process:
Stage 1: Bulk Melt. Removes the wax from frames, scraps, wires, etc, etc, etc,. Yields bulk chunks of wax with some impurities embedded. This is what your solar wax melter does best.
Stage 2: Remelt and Stratification. Separates the wax from other liquids, sand, dust, slum gum fines, other impurities. Yields near pure wax which is mainly light yellow to orange determined by colors of the pollens that are still entrained.
Stage 3: Remelt and Filtering. Removes ultra fine dust particles and pollens. Wax is passed through multistage strainers or pressure filters. Yields purer wax which is nearly white.
Stage 4: Remelt and Molding. Yields whatever you are making out of the wax. Candels, balms, body butters, sculptures, whatever.
For most users, stage 2 rendering, stratification, is good enough. Meaning layer out the impurities. Select a pan, pail, tub, whatever shape you want the bulk block to end up as. Add water so there will is 5 to 10cm or more of water in bottom. Add the wax chunks. Heat the container to melt the wax. When completely melted, give it a stir, then remove the heat and let it solidify slowly. The wax will layer as follows.
Top, 1, wax
2 slumgum fines, trash or fertilizer
3 honey, overheated/cooked, bakers honey or trash (do NOT feed to bees!, poisonous HMF)
4 water, trash
Take the solidified wax block out, flip it over, scrape/shave the brown stuff off the bottom and trash it. You are left with a clean pure wax block.
The lower liquid layers are also trash.
PS there is no such thing as overheated wax. Temperature does not change the properties or color of the wax. What is changing color is the honey and pollens in the wax as they are being cooked by the temperature. *** Monitor and control the temperature of the melters. Very hot wax is extremely flammable. Above 200 degC the wax can and will flash, self ignite, and burns violently.
Hope that helps!