If you want completely custom font colors,
I highly recommend SRD's amazing Custom Colors plugin.
Which is located here
The plugin sets the color of the font to the exact color code you want.
Note: When you hit preview, it won't show it. You will see in the actual game/test though.
That link to SRD's page even comes with a tutorial he made on how to use it.
To use SRD's Custom Colors plugin, you may need to have SRD's Game Upgrade plugin as well which is here
But along with what Ossra said, yes, yes, yes, use YEP's Message Core: here
To use YEP's Message Core though, you will need YEP's Core Engine: here
Hope this helps.