For some reason, which I don’t understand, the color of the page heading of my shop page (it’s the only page where I use the page heading; here with the categories menu) sometimes changes its color from black to light grey when filtering for a a product category. Can you tell me how to keep it in a constant color (black)? The pages heading background is set to black.
There is an option in our theme to upload page heading image for each category. Probably you have uploaded image for some category and it is shown when you open this category. Check this option in Dashboard -> Products -> Categories -> edit category.