The problem of the Venus orbit disappearing is caused
by the larger Earth orbit being drawn over it.
There are two possible ways to fix this problem:
1 - Draw the orbit of Earth before the orbit of Venus
2 - Change the fill color to transparent
by adding a fourth value to fill and setting it to 0.
The second method has been used here.
Notice that when the fourth value in fill is set to 0
the first three numbers have no effect
because the background shows through.