You should be able to change the color of your bars on a bar graph. Like on Excel Online, you can't change your bars different colors.
Good feedback. We’ll consider this for a future release.
In the online version of Excel it isn't possible to change the colour of bars in charts or graphs on the chart menu. You can't right-click to change them either. I use charts a lot in my work and need to be able to change the colours as easily as I can in the desktop version of Excel