I have never met with data about this but it is necessary to distinguish whether it is a sweat with acidic or alkalinity pH. There is a different composition and different fluid dynamics depending on the pH. Surely it will be affected on light absorption coefficient.
Article about this in on my RG profile 'Influence of the Physical and Chemical Properties of Composite Insoles on the Microclimate in Protective Footwear' FIBRES & TEXTILES