The invocation mantra that comes before the Vishnu sahasranamam begins as follows:
Shuklam Baradaram Vishnum, Sasi Varnam Chatur Bhujam, Prasanna Vadanan Dyayet, Sarva Vignoba Sandaye
Dressed in white you are, Oh, all pervading one, And glowing with the colour of moon. With four arms, you are, the all knowing one I meditate on your ever-smiling face, And pray, "Remove all obstacles on my way".
Q1) Who is being referred to as 'dressed in white' when Vishnu is pitambaradhara