The issue is the heat levels themselves.
From a link previously supplied to you;
Color is related to the frequency (or wavelength) of light. The visible spectrum runs from red, wavelength = 700 nm and f = 4.3 x 1014 to blue, wavelength = 400 nm and f = 7.5 x 1014.No go back to some of the other info regarding heat and metals.But temperature is also related to color. This is because hot things radiate light (for instance, the filament in an incandescent bulb). The temperature of the object affects the color of the light that is radiated. "Red hot" things glow red, "white hot" things glow white. How does this work? There are some complicated details, but here is the basis: as we discussed in class, temperature is a measure of the internal energy of a material. The hotter a material is, the faster its atoms are moving. But light is emitted when charged particles vibrate. If an electron or an ion (the core of an atom, including its inner electrons but not those involved with bonding) is vibrating fast enough, it may emit light. Clearly, the hotter an object is, the more often this will happen, and the higher the frequencies involved will be. Thus, a hot object that appears a dim red is cooler than one which is bright orange. An even hotter object will be emitting radiation across the whole visible spectrum resulting in a white appearance(for instance, the filament in an incandescent bulb). The exact distribution of colors emitted by a material at a given temperature depends a bit on the composition of the material. However, to a great extent it does not.
Then ask yourself -- what of the contents which were being heated? How would those react to the heat itself(?) irregardless of any imagined nuclear reaction.
Did you know that metal when heated -- can increase in temperature immediately after be taken out of the heat of a forge?
The raise in temp doesn't last long, but it is measurable.