There were some major changes in uniforms during the 1800- 1813 period. For the 1812-14 campaigns- the period I know the most about- Jager regiments, like the rest of the infantry, were pretty much standardized. For the Jagers it was black cuffs and collars piped red.
The devil is in the details. Shoulder straps would be red, green piped red. white, yellow or blue depending on the regiment's place in its division. I'm going from memory here, but I believe the number of the division would be embroidered on the shoulder strap. This may or may not be an issue depending on what scale figures you are painting.
There are contemporary prints showing Jagers with brass regimental numbers on the cartridge boxes.
No flags, though, as they are light infantry. They would have had hornists; basically the same uniform but with white lace down the sleeves.