Be able to declare a base color for a metric

[brendanheywood]

• [x] This would be a new method, don't think we need config for this
• [x] Each metric can define its own colors and for the moment these can be hard coded in each
• [x] Show a color swatch in the metric table in admin settings
• [x] Each each metric in its color
• [ ] If we are showing many lines, avg, min, max for a metric show them all in the color for that metric