unknown flag

[18TH TEXAS VOL INFANTRY]

General Sam B. Maxey's Daughter painted this picture for him after the war. The painting hangs in his home in Paris Texas, He formed the 9th Texas Infantry up in that area. They served in AOT, he was placed in Command of the Oklahoma Region.
I also observed a drawing of a similar flag in the book "Texans in Grey: The Regimental History of the 18th Texas". That black and white drawing also showed what appeared to be a 2nd National Flag with a reverse Taylor flag in the upper corner The cross was done a lot lighter than the back field as would be the case with the Taylor Flag. As the Taylor flag was the reverse of ANV Battle Flag it would be possible that 2nd National versions where produced?
Has anyone ever seen these.
I don't believe the General's daugher would have painted something that he would display so, if it never existed. It may have been the General's personal flag, however the 18th served in the Trans-Mississippi, not with Maxey. Some of Maxy's Cav. did support operations in that region and may have brought the flag with them
There are only two know Taylor flags, both in Texas they are 6' X 6' square, (everything is bigger in Texas) but none of the flag in the painting.
The flag features a reversed color - General Richard Taylor

[Alabaman]

Hi 18th Tx vol. Inf.!,

I had an ancestor, a Captain, in Parsons Texas Ranger <Cavalry.> I doubt think this would be their standard but I'll check for other ideas. It's too big for a cavalry banner; 6'x6'.

This is a beautiful painting, BTW! If I find anything I'll certainly contact you.

Thanks for sharing the painting & info, Texas!

Sincerely,
Alabaman