Sure it's I./7. JG26?
III./7. would be correct, but this was not reported to be on Eastern front.
First Gruppe has 1st, 2nd and 3rd Staffel
My sources say 3. Staffel of I. Gruppe, simply Yellow Numeral denotes 3rd Staffel (the last) of 1st Gruppe
The Paintscheme is reported to be initially in Channel colours, arriving at the Front it went thru Workshops
for neat new garment, carried out evenly. I bet my Ass sth. like the Charkov facillity, or the successor of that Maintenance Station.
Where they pooled up arrivals, being refurbished as they went to the Front.
At some parts the old paintscheme was left.
There is a sure sign the other Staffel Kites had a similar paintjob from 1 to 12, or how many they used up.
If you have Log Book from that Pilot his Kite Number could be allocated properly. Or maybe a Staffel wartime Diary, sometimes Info
can be found there too.
This is a fairly evenly carried out refitting, I know pictures of SG replacements that got patched up
like a clown plane, Numerals on the Tail, overpainting the Swastika, patched up Civil regisration and former Unit Markings.
Inside my Schlachtgeschwader Skinpacks.
Update:

Seiferts Plane in Belgium as Commander of 1st Gruppe, a Command he followed in the East, being later succeeded by Losigkeit

He flew with the same Markings as CO and Stab of I. Gruppe. A 7th Staffel followed up, but was a different Shoe.
Just count his Tally before the move to East, carry out the refurbish, masking some parts like Yellow 5
and you have the actual Plane. New Eastern Kills they got marked white, while the detailed Western got untouched as applied.
Is a simple Skin job to do.
If you need assistance, further Help, call me, I'm on Home Office this Week.
Best wishes
Tobias