61 of 100: BEST BEE

$\large{\begin{array}{ccccccc} && & &\color{#D61F06}B & \color{#3D99F6}E& \color{#69047E}S&\color{#20A900}T\\ \times&& & & & &9&9\\ \hline & & \color{#D61F06}B & \color{#3D99F6}E & \color{#3D99F6}E& 5& 5&1 \end{array}}$

If each letter represents a different nonzero digit, what must $\color{#D61F06}B$ be?

Our cryptogram puzzles are getting tougher, and they will get tougher yet before the summer is over!