Thank you Mr. Adams for the photo links!!!
I have been looking for photos of mounted Naval Officers in field gear for a very long time. The second last photo of the third link is the answer to a prayer!!!!!
Of course now I've go to "photo interpret" the picture. It's of an LCDR and a Surgeon. The Surgeon looks like he's wearing a Marine Corps shirt with an armband (possibly Red Cross). He does not appear to be armed. He is wearing a shoulder board that appears "soft" but that may just be distortion. He's also wearing a Campaign Hat.
The LCDR appears to be wearing a dyed SDW blouse and trousers, with leggings. I can't tell if he's armed or not, but his blouse is clearly "belted." He might be wearing a sword on his left. He's wearing a Fedora and it has something on the front (Eagle, Globe, and Anchor; did he borrow the hat from a Marine?). The photo quality is just not good enough to tell for sure.
Behind the LCDR there appears to be a mounted Chief in un-dyed whites.
The LCDR seems to be riding an English-type saddle; the Surgeon may be on a Mac. I'm not familiar enough with them; the rigging doesn't look right, but then maybe it is.
The LCDR's horse is carrying a bit and bradoon, but I don't think the bridle is an M1909 (but it might be; the detail just isn't good enough to be sure). My guess is that it's a civilian bridle. The Surgeon's horse looks like it's carrying a civilian bridle with a "Tom Thumb-type" bit.
IIRC the 1907 Uniform Regulations permitted the Captain of a ship to authorize enlisted members of the landing force to dye up to two uniforms khaki. In a later document the ship was permitted to purchase two bottles of dye for this purpose. I would not be surpised that coffee or tea might be used as a dye in the abscence of a formal material.
These photos are Mondo Kool!!!!!
SQQ