Question

Why gold nanoparticles change their color with decreasing size?

Answer 1

When synthesizing gold nanoparticles using the Turkevich method, the colour of my solution turned from a light gold solution to a dark violet to a red colour. But since the particle size should increase over time, should the wavelength the nanoparticles absorb shift to the red end? And so initially when citrate was added shouldn't the lower wavelength lights be absorbed first so red colour should be reflected, and after a while when the size of the nanoparticles increased longer wavelengths would be absorbed and so a dark violet colour would be reflected.
So shouldn't the colour trend be red -> dark violet? Why does the opposite happen?