Srimate Ramanujaye Namaha!,
Vedas should be accepted based on the efficacy of already proven concepts they have given 1000’s of centuries ago, ( some of which are proven by modern science in recent years) ..like disinfectant property of cow dung, gomutra, eclipse and planetary movements and speeds.
When we cook rice , we will assess only one sample of one rice particle to assess if it is cooked. Similarly base don the the already proven vedic practices ( more examples can be given in this corona period..Namaste, washing hands, legs and bathing after travelling out etc).
Coming to this specific question..let me try to provide some reasons..
Black object absorbs most of the light that falls on the object and reflects none or little , that is why it appears black.
Light( Sunlight is the source of all light directly or indirectly) is considered to be source of purity and knowledge and helps one come out of ignorance.( Easy to relate in corona year)
So the actual light around a black dress is reduced, it does not reflect the light to the person wearing it or to the people nearby. So the amount of light (sunlight) purifying the person reduces.
Secondly, all things in this world are classified as Sattva- Rajas and Tamas- Goodness, passion and ignorance. So examples would be white, red and black. Black being a tamasic colour (may be due to above reasons) is not recommended.
P.S: an interesting argument would be Krishna or perumaal is black..but they are not material black but are a spiritual black, where even though they are black, they radiate brightness equivalent ot 1000’s of suns. so we may not be in a a position to discuss that..