Created attachment 217100 [details] 12 excamples In excamples 1,2,3 and 4 without border-collapse:collapse the table border is around the cell borders. Line width increases from 1 (2) over 2 (3) to 3px (4). In 5 to 12 border-collapse is defined and the cell borders fell together. But with the alpha they should blend each other. Instead Webkit decides which border dominates the other cells and draws only one color. On the corners this dominant color is applied two or four times, on the inner edges two times. 5 to 8 have a transitional declaration, 9 to 12 not. The table border is only visible when the line width is thicker than the one of the cell borders (12). And the outer cell borders are not visible. Why not? For another excample see Bug 124441.
Created attachment 217102 [details] html docs