Do you have FileMaker 12 or an ealier version?
This method works for all versions:
Create a layout and set it up for list view.
Remove the body layout part.
Add a new layout part, a SubSummary layout part "when sorted by Color"
Add a summary field to your table that counts a never empty field such as a primary key field or this color field.
Put the color field and this new summary field in the sub summary part.
Find the records you want for your report.
Sort them by the color field.
You now have a report where each different color makes up one row of the report and the summary field shows the number of records with that color.
If you have FileMaker 12, you may be interested in using ExecuteSQL to produce this type of information: FMP 12 Tip: Summary Recaps (Portal Subtotals)