ggplot gallery, guidelines, axes section, color scheme

[OskaratOmni]

reviewer comment: in the Axes section plus FIRST chart titled "4-Cylinder vehicles get better gas mileage on average." small thing but I wonder if we should have the bars be all the same color? I think this would better align them with our color guidance since the colors aren't really needed in these bar charts.

• typically we have one or two bars that are emphasis colors (teal or blue) and the rest are grey - we don't have bar charts where each bar is a different color (see template examples)
• even tho the guidance is about axes, please edit to have eitiher all bars a grey color or one bar emphsaized with an accessible chart title like "4 cylinder cars have higher mpg than 6 or 8 cylinder cars" [since this is an mtcars example the specifics of the title aren't too important].
• we do sometimes say things like "all groups were represented in the sample" with all the bars the same color, but typically we have an emphasis or call out color a group or two.

Likewise, the typical OMNI graphic will have a graph title that is color coded to match the bar that is being emphasized in the bar chart.

Can this be added to the general guidance?

[dgkeyes]

I've made the changes. I also changed a few of the other graphs to make things more consistent.

Please see https://stupendous-biscuit-9f1c75.netlify.app/ggplot-guidelines. @OskaratOmni let me know what you think.