As you know, the 3rd was marching and camping since early June 1861. Knapsacks containing spare clothes were discarded in the march to Camp Jackson. While the Regiment was complimented on their "fine military appearance and bearing" a month after their arrival in Arkansas, it was another month of marching until they reached Wilson's Creek. Tunnard makes no mention of appearance until after Wilson's Creek. That is when descriptions of their rough appearance begin.
Here is the first citation:
William F Tunnard "Southern Record: The History of the 3rd Reg. Louisiana Infantry" (Morningside Edition)
p.81 September 1 1861 "soiled and tattered uniforms"
p.85 makes similar mention.
William Watson, "Life in the Confederate Army" (Time-Life Edition)
p.215 An encounter with US Regulars in the morning of the battle where neither side knew at 40 yards what side each force is interesting.
p.233 Immediately after the battle "a uniform appearance so far as being threadbare, and dirt and raggedness made them much alike."
I seem to remember an account from the O.R's where the 3rd were described as being mainly in gray uniforms.
Regarding early 1861 uniforms evidence is scant. The Winn Rifles and Shreveport Rangers were donated shirts and pants by the ladies of New Orleans. In a photograph Corporal D. March of the Caldwell Guards wears a dark kepi with a darker band, a gray 8 button coat with dark tape around the collar base and plain cuffs. The Pelican Rifles, the ladies of Baton Rouge supplied then with 96 pairs of pants in May 1861.
Many companies found it impossible to procur the materials for uniforms in 1861 - sources of things such as buttons, hats and military cloth dried up at various times due to the demand across the South. Some clothing businesses did manufacture full suits of uniform clothing - One firm (I think the name was Folger) made 2500 suits after the pattern of the Louisiana Regular's fatigue dress in the hopes of attracting the State contract. When they didn't these were offered on the public market. This could account for descriptions of blue uniforms.
Hope this helps.