As José Andrade pointed out,
Amplitude is just how strong the light is.
However, there is a problem with José's assumption that:
the color does not change. They look the same.
And @Not_Einstein is right when he writes:
as the intensity is one component of color, the color will change. Maybe not the hue, but the color will. Bright red is not the same color as dim red.
But the problem is actually even more complex than that.
Very few monochromatic lights conserve the same hue when their intensity changes. You can see that with LEDs: in a white room with no other light source, have a look at the color of the light projected by a blue LED situated, say, at 5 cm of a white wall. Then look at the color of the light projected in the room: they are different. The high-intensity blue light is blue, the low intensity light is violet.
This difference in hue exists for most wavelengths. As far as I can tell by my own experience with monochromatic LEDs, the only "hue stable" lights will be
violet (between 380 and 430 nm),
blue-green (around 490~500nm, and probably slightly different for each individual),
yellow (around 570~575nm - probably slightly different for each individual) and
far red (between 640~650 and 700nm). Other monochromatic lights tend to change in hue when the intensity of the light changes.