First to go on board with partners securing success (5)
I believe the answer is:
white
'first to go on board' is the definition.
I can't tell whether this definition defines the answer.
'partners securing success' is the wordplay.
'partners' becomes 'we'.
'securing' is an insertion indicator.
'success' becomes 'hit' (hit is a kind of success).
'we' placed around 'hit' is 'WHITE'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for white that I've seen before include "Outer part of egg" , "See 10" , "and 9: What Bing Crosby dreamed about" , "Colourless" , "11's domicile" .)