This is a wild raspberry bush outside my front door. I have a love-hate relationship with it because it's fruit is delicious but it has wicked thorns. However, you can see here that there are two distinct variations in color on the plant. The leaves closest to the wall are very dark green, the same color they are in summer, and the rest of the leaves are varying shades of yellow and light green. I surmised that this color contrast results from unequal exposure to sun. Indeed, the darkest leaves seldom get sun due to the angle of shadows in the afternoon. The white wall behind the plant is southerly and the red brick wall is on the west side.