The 'imputed' heatmap uses the most elaborate color scheme:
Site/time combinations that are observed are colored red, the higher the count, the darker the red.
Site/time combinations that are imputed are colored blue, the higher the estimate, the darker the blue.
For the 'data' heatmap, missing site/time combinations are colored gray.
For the 'fitted' heatmap, all site/time combinations are colored blue.
By default, all counts are log-transformed prior to colorization, and observed counts of 0 are indicates as white pixels.