Shiva Purana

siva.sh/siva-purana/rudra-samhita/12/71

तथा च मलिने वस्त्रे रंगः शुभतरो न हि ।। क्षालने हि कृते शुद्धे सर्वो रंगः प्रसज्जते ।। ७१ ।।

sanskrit

If there is dirt in the cloth the dyeing process cannot be carried out effectively. After the cloth is bleached any dye can be applied to it effectively.

english translation

tathA ca maline vastre raMgaH zubhataro na hi || kSAlane hi kRte zuddhe sarvo raMgaH prasajjate || 71 ||

hk transliteration by Sanscript