Normaly, no french troops on the eastern front wear bleu horizon uniform. Before 1915's winter, metropolitan troops wear exactly the same uniform of the begining of the war with red troosers.
Colonial troops wear high colorred uniform from armée d'arfrique.
After 1915's winter, all french troops on the eastern front wear Kaki-Moustard uniform and adrian helmet.
French troops in Dardanelles (and Macedoine/ Salonique after dardanelles) wore the same dress than in europe, with a little late. Colonial and metropolitan troops were dressed with dark blue dresses mixed with new BH dresses. The troops sent to Gallipoli were new recrutes (classe 1915) from depots from all regiments (one bataillon from 105 de ligne / Riom for exemple) and dresses with new equipments.
for exemple :
One of the "white" colonial regiment in Gallipoli (image from National australian army museum) BH coat with old fashion dark blue trousers with red piping

Very famous photo summer 1915 in Gallipoli the man wear entire bleu horizon dress:

well known photo again : all soldiers wear BH dress with velvet trouser for the second, and an ancient "patte d'épaule à rouleau" (shouder patch) in dark blue. All equipment are the ancient black patern (the brown one start to be deal mid 1915) source : IWM

for colonial "white" troops and senegaleses :
White guys are in BH coat with old fashion dark blue trousers with red piping as in métropole

senegaleses are in old blue fashion

senegalese in dark blue 1914 coat :

Zouaves :
territorial zouaves (front right) with old fshion zouave bolero with speecial cartridge box, the trouser seems to be the new paterne in khaki "moutarde" they are keeping turkish prisoners.

Zouave bataillon in "moutarde" kaki dress

Territorial units and of campaign (winter1915) keeping prisoners : new dress for the winter1915 : BH coat with khkaki pants and jacket under the coat, like in France.

best regards
Paco