Basic Color Genetics: Chestnut Agouti and Opal

Chestnut is the agouti version of black.   
The color genes are: A-B-C-D-E-
In translation: Agouti pattern, black family, full colored, dense color (non-dilute), extended color. 
All these are dominant, the - means there maybe another same dominant gene or a recessive gene.
The word chestnut is a very good description, it's brown/orange with black tips.  Color of the eyes: Brown   This is Lipton.

This is Lipton again but photo taken in the shade to compare the influence of the lighting.

A good chestnut should have very definitive ring pattern.  This photo of Lipton was taken when he was a junior.   It's harder to get the pattern as sharp as this when the senior coat comes in.

This is Lipton's dad William Penn who is an opal.  Opal is the dilute version of Chestnut Agouti.
The color genes are: A-B-C-ddE-
In translation: Agouti patterned, black family, full color, dilute color, extended color.
The only difference between the chestnut agouti and opal is that the chestnut is non-dilute while the opal is the dilute.  Color of the eyes: Gray.
Opal is an established name used in the ARBA Standard of Perfection, genetically opal is "blue agouti", the agouti version of blue.     

This is again William Penn, photo taken in the shade.  It's more bluish with tan color underneath.   The ring pattern will not be as obvious as chestnut agouti due to the dilute factor.   Since I did not own William Penn when he was young, I do not have any photo depicting his ring pattern.   

 This is a days old opal baby, it shows blue with tan undertone and a white tummy.   

To reiterate: Chestnut Agouti color genes:         A-B-C-D-E-

                     Opal (blue agouti) color genes:     A-B-C-ddE-

Since offspring takes a copy of the gene from each parent, Lipton is William Penn's son so Lipton inherited one copy of the dilute gene d.   Thus Lipton's color genes are: A-B-C-DdE-