Intermittently, over the last five or six times I have used plot and histogram the colors of the figures are wrong. When I assigned colors and when I didn't. If I restart Matlab the problem is sometimes resolved. The wrong color scheme appears to be green at the bottom of the figure, black in the middle, then red at the top. Sort of fading from top to bottom.
lambda = 5;
p = poissrnd(5,1,1000);
h = histogram(p,'Normalization', 'probability');
Notice how the bottom has that green fade.