The Instance Color texture holds an image, and it prepares to map each pixel to geometric instance IDs.
Figure 1: A color texture map applied to instances with the Instance Color texture node
Figure 2: A cube and 99 instances of the same cube are shown here, forming a 10x10 grid of cubes
You can plug an image with 10x10 pixels into the Instance Color texture to match these dimensions. OctaneRender® maps each pixel and assigns them to the instance IDs.
Figure 3: 10x10 grid with four colors