HEAT COLORS
MILD STEEL
2500 F 
1371 C MAXIMUM HEAT FOR WROUGHT IRON FORGING, STAINLESS STEEL MELTS (2400 to 2700 F)
2400 F 1316 C MILD STEEL BURNS, CARBON STEEL MELTS 2400 (HIGH) TO 2750 (LOW CARBON) F, GLASS MELTS 2377 F
2300 F 1260 C MILD STEEL MAXIMUM FORGING TEMPERATURE & FORGE WELDING HEATS
2200 F 1204 C
2100 F 1149 C GREY CAST IRON MELTS FROM 2100 TO 2350 DEGREES F
2000 F 1093 C GOLD MELTS @ 1945 DEGREES F
1900 F 1038 C COPPER, BRASS, BRONZE MELT 1652 TO 1981 DEGREES F
1800 F 982 C SCALE FALLS OFF IRON FREELY @ 1750 DEGREES F, GLASS MELTS 1800 TO 2200 DEGREES F
1700 F 927 C SILVER MELTS @ 1761 DEGREES F
1600 F 871 C
1500 F 816 C UNFANNED COALS OF A WOOD FIRE APPROX.
1400 F 760 C SCALE FORMS AND ADHERES TO IRON, MILD STEEL MAGNETIC POINT (1420 F)
1300 F 704 C BORAX MELTS @ 1365 DEGREES F, ENAMELS FIRED AT 1350 TO 1500 DEGREES F
1200 F 649 C IRON FINISHING HEAT & STRESS RELIEVING, ALUMINUM MELTS @ 1220 DEGREES F
1100 F 693 C RED IRON, VISIBLE IN SUNLIGHT, STRESS RELIEVING OF IRON
1000 F 538 C RED IRON, VISIBLE IN DAYLIGHT
PERCEIVED COLORS DEPEND ON LIGHTING
Aluminum:
The steel chart didn't copy exactly but you can figure it out. As you can see, at certain temperatures the two would be almost indistinguishable. Not to mention the fact that the colors can look different in different lighting conditions. Maybe I'm missing something, and I'm sure someone will correct me if I am, but it seems to me that it would be pretty hard to tell the two apart at certain temperatures just by looking at them.
