My grid has developed over the years, to the point where I took the (very long) time to sit down on Photoshop and design it properly.
It has 20 by 20 boxes and each box has an additional 16 boxes in in of a different colour. There is a layer for the main grid in Pink, one in Black, one for the fine grid, one for the numbers, and the background. There are all seperate so you can adjust the opacity, and only show your desired layers.
If you prefer a different colour, just click and hold CTRL or Command and select that layer, create a new layer, then press G and click on the selected area. with your chosen colour.