Many users and most colorblind users have difficulty distinguishing RED from dark colors (like black text on a red background) and difficulty distinguishing GREEN from light colors (like green versus yellow or white text on green background). To improve readability for all users, use white text within RED backgrounds/buttons. Use black text within green and yellow backgrounds/buttons. Highlight red arrows on black backgrounds with a white shadow and highlight yellow or green arrows on white backgrounds with a black shadow. Finally, and most importantly for colorblind users, use a shade of green that has significant contrast next to yellows or allow colorblind users to substitute a different color for reds, greens, yellows consistently throughout the UI. Enabling a user to increase the line size would also help distinguish when lines transition to / from green and yellow.