You may be interested in the Grey's Magic for Image Computing (G'MIC) plugin for Gimp. In their collection of Arrays & Tiles plugins you will find the Array [random colors].
- Opacity: controls the amount of variation induced by random colors.
- X-tiles, Y-tiles: control the number of resulting tiles (maximum 20).
In addition various color variation effects different to tiles are also included, e.g.:
Film grain
Random Gaussian noise degradation
Random color ellipses pattern