Reserve Bank of India has introduced the new ₹ 50 denomination banknotes in the New Mahatma Gandhi Series, bearing signature of Governor of Reserve Bank of India Dr. Urjit R. Patel. The new Rs 50 Note has base colour of Fluorescent Blue.
New Rs 50 Note
RBI also states that the existing Rs 50 notes to continue to be legal tender.
Dimension of the New Rs 50 banknote is 66 mm x 135 mm
You can check more details of the new bank note of Rs 50 at RBI site here