Regiments in the Duchy of Nassau

They had 2 regiments of infantry. The 1st and 2nd Nassau Regiments.
They wore green uniforms of French style with Yellow lace and black cuffs and collars. They had yellow leather equipment belts. Their grenadiers had black fur colpacks.

There was a jager detachment that was formed in 1813 which was small (about 2 companies strong) who wore a similar uniform to the line infantry.

There was also a Nassau light horse unit (chassuers) who served Alongside the French army. They wore French style chassuer dress with black cuffs and I think white lace which made them quite distinctive from other French units.

Each regiment was of 3 battalions.

However in 1806-7 they had different uniforms. And organization. 1806 their infantry was orginized as follows.

1st battalion. Lieb Battalion Von Todenworth.
green jackets, orange cuffs and collars with grey trousers. Yellow belts. Black crested Bavarian helmet.

2nd Battalion. Von Kruze.
Green jackets with red collar and cuffs and yellow lace. Black bell top shako. Yellow belts.
Green trousers.

3rd Jager Battalion. Von Schaffer.
Green jackets. Black bicornes. Red collars and cuffs. Black cross belts. Grey trousers. Rifles.

4th battalion Von Holbach.
Green jackets. Green bell top shakos. Yellow cross belts. Grey trousers. Red collars and cuffs.

https://www.brigade-uniform-tafeln.de/search?sSearch=Nassau+

If you want full uniform guides you can buy them if this guy.