As far as I'm aware the 84th Line wore regulation French infantry uniforms throughout the period you mention.
Courtesy of http://www.napoleon-series.org/milit...renchinf9.html
84e Regiment d'Infanterie de Ligne
Regimental History
1684: Created Regiment de Quercy
1776: Regiment Rohan-Sourbise
1787: Regiment Rohan
1791: 84e Regiment d'Infanterie
1794: 84e demi-brigade de bataille (formed from the following)
2e bataillon, 42e Regiment d'Infanterie
2e bataillon, Volontaires du Cantal
4e bataillon, Volontaires de Rhone-et-Loire
1796: 84e demi-brigade d'Infanterie de Ligne (formed from the following)
36e demi-brigade de bataille (2e Bat 18e Regt d'Inf, 1er Bat Vol du Loiret and 5e Bat Vol de la Somme)
116e demi-brigade de bataille (2e Bat 58e Regt d'Inf, 2e Bat Vol de la Moselle, and 1er Bat Vol de Lot-et-Garonne)
1803: 84e Regiment d'Infanterie de Ligne
Colonels and Chefs-de-Brigade
1791: Buonavita (Joseph de) - Colonel
1794: Briqueville (?) - Chef-de-Brigade
1794: Lespinasse (?) - Chef-de-Brigade
1796: Quetard de la Porte (Jacques) - Chef-de-Brigade
1800: Sancey (Joseph) - Chef-de-Brigade
1803: Charnotet (Jean-Baptiste) - Chef-de-Brigade
1803: Sancey (Joseph) - Colonel
1808: Gambin (Jean-Hugues) - Colonel
1811: Pegot (Jean-Gaudens-Claude) - Colonel
1814: Wautier (Charles-Albert de) - Colonel
1815: Chevalier (Pierre-Andre-Remy) - Colonel
Three of the above officers attained the rank of General-de-Brigade
Charnotet, (Jean-Baptiste)
Born: 17 September 1761
Chef-de-Brigade: 13 January 1800 (89e demi-brigade d'Infanterie de Ligne)
Chef-de-Brigade: 24 September 1803
General-de-Brigade: 8 March 1807
Officer of the Legion d'Honneur: 14 June 1804
Baron of the Empire: 20 August 1809
Died: 5 November 1843
Gambin, (Jean-Hugues)
Born: 15 May 1764
Colonel: 25 December 1807 (53e Regiment d'Infanterie de Ligne)
Colonel: 1 May 1808 (84e Regiment d'Infanterie de Ligne)
General-de-Brigade: 5 March 1811
Count of the Empire: 26 April 1809
Died: 18 May 1835
Pegot, (Jean-Gaudens-Claude)
Born: 6 June 1774
Colonel: 19 April 1811
General-de-Brigade: 1 January 1814
Commander of the Legion d'Honneur: 5 February 1813
Died: 1 April 1819
Colonels killed and wounded while commanding the 84e Regiment d'Infanterie de Ligne
No Colonels killed or wounded
Officers killed and wounded while serving with the 84e Regiment d'Infanterie during the period 1804-1815
Officers killed: Thirty-six
Officers died of wounds: Ten
Officers wounded: One hundred and twenty-seven
Regimental war record (Battles and Combats)
1792: Valmy
1794: Oneille
1795: Saint-Martin-de-Lantosca
1796: Borghetto, Mantua, Cerea, and Bassano
1800: Engen, Moeskirch, and Hochstedt
1805: Ulm and Austerlitz
1809: Sacile, Prewald, Graetz, and Wagram
1812: Ostrowo, Smolensk, La Moskowa, Malojaroslawetz, Krasnoe, and La Beresina
1813: Feistritz, Laybach, Isonzo, and Caldiero
1814: Verone, Mincio, and Plaisance
1815: Waterloo
Battle Honours
Ulm 1805 and Wagram 1809
As far as I know they were never reclothed in the 1806 white uniforms but if they had been they would have worn Grass Green facings on the cuffs abd collar only, brass buttons and horizonal pockets,
Flag of the 84e régiment d'infanterie de ligne (84th line infantry regiment) of French army, with its battles.