What did you call trousers ? chausses ? If it's the case, the most popular material is wool, and after that silk, linen could be use, but we don't have evidences of colored linen for that use. Leather was sometimes use as a material, but for renforcement of others materials, and not alone (or it was very uncommon).

And I speak for the late medieval period. Medieval times: 1000 years, that's big.

I know in the 18th and 19th centuries leather breeches were desired by many in the working class. As one Irishman put it 'they wear forever and look elegant after that'. No washing or laundry required which was a saving of money. Certain occupations were known for wearing leather breeches but I forget which ones. Possibly looking after horses?

How far back this goes, I can't say.

The Museum in San Fran gives a long range for these leather trousers, but the XVI C is included in that range.

Here is a very complete list of leather clothing throughout the middle ages. Of note:

1250 - > It seems quite proper also to wear trousers [hosen] of black fur [leather],

1450 - >For j dakyr of hose ledder, viij d
(hosen leather)

Mid 16th c ->A leatherworker's inventory of Kitzbuehl describes several sets of trousers, in connection with the word "Gesaess" or "seat." Such trousers (whose length is unclear but likely went to below the knee) were either made entirely of leather (perhaps chamois) or were made with a leather front and woolen back or vice versa. The inventory describes at least one pair as "old leather trousers

So, you are good!