Cell fill colors in Excel 2010

I could not find a built-in way to make a specific fill color available on the ribbon. The way I would do this is to write two macros and put them in your PERSONAL.XLSB macros, then add buttons on the ribbon to call them. Here is an example that fills the selected range with red. (Your title and last sentence refer to "fill color" so I assume that's what you want. Your first sentence says "font fill colors" but font color and fill color are two different things.)

First, hit ALT-F11 to open the VBA development window.
At the left is an object navigator. You should see an object for PERSONAL.XLSB.
Right-click on its name and select Insert, Module.
Now you see a new line item, probably called, Module1, and the window to the right will be a code window for that new module.
Paste this code into the code window:

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Right-click anywhere on the ribbon. Select Customize the Ribbon.
Above the list on the left is a dropdown. Select Macros.
Look for the macro PERSONAL.XLSB!FillRed, and click it to highlight.
On the list on the right, click on the + sign next to Home, then click on Font.
Under the list, click on New Group. You can then click Rename to name the new group whatever you want. I called it "Fill Colors". This is the group name that will be shown on the ribbon.
Single click on your new group, then click the Add button in between the two lists.
On the list on the right, click on the name of the macro you just added. Click on Rename to rename it and select an icon for it. This is the name used to display it on the ribbon.
Click OK.
Now you have a new panel on the ribbon under the Home tab that has your new fill color button.
Repeat the procedure to add other macros for other colors.

If you want these buttons to be on the Quick Access Toolbar instead of or in addition to the ribbon, you can add the same macro by following a similar procedure, clicking on Customer Quick Access Toolbar instead of Customize the Ribbon, and follow the same steps.