Rall was formed from the grenadier companies of the Land Miliz, which were permanent and hence the grenadiers carried colours as they were permanently detached from their parent units (unlike the grenadiers of ordinary "line" regiments).
Woellwarth existed from June 1777 to July 1778, and was formed from the survivors of Rall's brigade (his own regiment and the fusilier regiments of Knyphausen and Lossberg, later Alt-Lossberg). After that point, the unit was divided back into its component parts.
Trumbach took over the grenadiers (d'Angelleli only existed from 1782 onwards), whilst Loos took over the Lossberg and Knyphausen personnel; however, the Knyphausen survivors/replacements went to Canada during the winter of 1779/80.
The question of uniform is intriguing - there are no records of any different, or distinctive clothing being issued to the Woellwarth unit, so presumably the men wore the uniform of their parent corps. My guess would be that the men who eventually morphed into the Trumbach regiment would have retained the Rall uniform, as it was normal for a unit to keep its original facings when the inhaber changed (only one Hesse Cassel regiment changed its facing colours during the war, also reverting from fusiliers to musketeers).
As regards legwear, it appears that the Hesse Cassel troops were required to retain their long gaiters and breeches almost through to the end of the war, and certainly whilst in garrison. Indeed, there is evidence that the Erb Prinz regiment was so attired at Yorktown, although the other HC regiment present during that siege, von Bose, may well have worn British-style overalls having served under Cornwallis from just after the siege of Charleston, SC as both they and Ewald's jaeger company were re-equipped from British stores. So probably NOT overalls for Trumbach, I'm afraid.