Hi,
first the Boxer Rebellion was an emergency alert for the colonial powers.
So they did send available troops in a hurry.
There were the big russian and japanese contigents. They did wear home service dress for the summer.
For the russians it is possible to use the figures of the WWI or the russo-japanese war of 1905.
The russian infantery and artillery in white litewkas. And the cossaks in blue or green. Donkosaks in blue, Terek cossaks in green.
The japanese same uniform as of 1905 - all in blue.
The british did send in the first wave a lot of Indian troops. It is reported that a Punjab soldier was the first one who entered the City of Peking through one of the gates.
(It was a storming of different City gates by the contigents and later confusing street figthing).
This Indian troops did wear their Khaki uniforms.
The Royal Marines like this
https://www.google.de/imgres?imgurl=https%3A%2F%2Fi.pinimg.com%2F736x%2F71%2F9f%2Fd1%2F719fd1eca30efbc121ea9de271f33c2b--la-rebel-boxer.jpg&imgrefurl=https%3A%2F%2Fwww.pinterest.co.uk%2Fexplore%2Froyal-marines-uniform%2F&docid=gVNchfKaucWXiM&tbnid=inKUsxye0qvR9M%3A&vet=10ahUKEwjXhZrir7LZAhUPb1AKHZzRCaAQMwhEKAowCg..i&w=169&h=225&bih=918&biw=1920&q=british%20marines%201900&ved=0ahUKEwjXhZrir7LZAhUPb1AKHZzRCaAQMwhEKAowCg&iact=mrc&uact=8The ship detachments sailor uniforms with straw hats. (Ochel fiugures are good)
The French marines did have the colonial uniform- blue uniformcoat. white trousers with a white helmet (for Tropical climate) The use of britich Regulars (same at Ochel) is possible with the difference that the French have nearly knee high boots.
Later colonial troops from afria did arrive. That were Zouaves and trailleurs senegalais.
The detachments from the ships were the matelots with their famous uniforms - the blue cap with the red bommel.
But there is a strong possibity that whiet Tropical helmets were worn, too.
For the Germans there are the marines from Berliner Zinnfiguren. But it is reported that the dtachments from the ships did wear their blue homeserviec uniforms.
They were first in figthing in Tientsin were they did have problems with the heat. They had to go this way to Peking, too.
The III. Seebataillon remained in Tsingtau.
Later the contigent witch arrived wit Graf Waldersee did have nearly same uniforms same the uniforms of the Schutztruppe (Ochel and others have them) in German-Southwest Afrika.
But I did see some photos with officers of the contigent with Pickelhaube. No joke.
For the americans it is possible to use 30mm flats from the Indian wars. But they did wear garters instead of boots. Figures of WWI are possible, but at his time they did have another Equipment and differen backpacks. It is up to the figure.
For the austrians and the Italien I do not have closer informations.
By the way the boxer Rebellion did not end with the conquest of Peking. It lasted many month more. There was heavy figthing in Mandschuria. In Autumn and Winter the antiboxer Troops did wear their wintercloses. In this figths were especially russsian, german and japanes troops involved.
In the south was some uprisin of Course. The French and the British did manage it with their lokal troops.
Regard
Zinnmartina