I am not an authority of IJN, so writing reliable information first.
At first, Type 93 intermediate trainer was painted silver and tail was painted red. Painting's having changed into the orange depends on the notice on December 29, 1938. Green camouflage was painted in 1944.
Then I'm able to say only uncertainty information, willows float planes was not in-land China areas.
As a result of searching, most of practice Air Squadron was in Japan at that time. There were also in Korea, the Kainan island, and the Philippines but it seem not to have been in mainland China. The number of seaplane practice Air Squadron unit was little, and all of those seems to have been in Japan.
In many cases, the novice pilot's training is is done by the safety areas. No novice American pilot training in Iraq and Afghanistan, you know.
IJN seaplane forces was mainly used in islands of Southeast Asia until the airport is constructed. I think the operation of seaplane to be limited very much in the inland China area.
Of course, a part of Type 93 were disposed to front-line troops and used as utility plane, I cannot be denied existence at all.
However I don't recommend the seaplane to add your diorama at least.