If you are coloring a patch, and the color “leaks” into other parts of the block, it indicates a drawing error.
If you lose lines, or the whole block colors at once, you have a line that is not connected properly in the drawing.
If you are unable to color all of the background then you may have mis-drawn patches or not filled the background completely.
If you cannot color a patch and the patch shows only as lines on the Color tab, then your patch is not closed.
If you cannot see a patch, it is possible the patch is hidden beneath another larger patch. Send the larger patch behind to change the layering order.