Maybe there is a solution. But, for that I assume there is an upper bound in the number of rounds needed, say n, and that the value b is fixed upfront. Then, there is the following EMSO formula,
$\exists L_{1} \exists B_{1} \exists R_{1} ... \exists L_{n} \exists B_{n} \exists R_{n} \phi(L_{1},B_{1},R_{1} ...,L_{n},B_{n},R_{n})$
where $\phi = Seq_{1} \wedge Seq_{2} ...\wedge Seq_{n}$
$Seq_{1}$=$\forall x (XOR(x\in L_{1},x \in B_{1})) \wedge empty(R_{1}) \wedge$ $lessthanb(B_1) \wedge IndSet(L_{1})$
If i is even :
$Seq_{i} = empty(L_{i-1}) \vee (equals(L_{i-1},L_{i})\wedge
\forall x ((x \in B_{k-1} \vee x \in R_{k-1}) R_{k-1})$
$ \Rightarrow XOR(x \in B_{k},x \in R_{k})))
\wedge lessthanb(B_i) \wedge IndSet(L_{i}) \wedge IndSet(R_{i})$
If i is odd (i $\geq$ 3):
$Seq_{i}$ = $empty(L_{i-1}) \vee (equals(R_{i-1},R_{i})\wedge \forall x ((x \in B_{k-1} \vee x \in L_{k-1}) L_{k-1})$
$ \Rightarrow XOR(x \in L_{k},x \in B_{k}))) \wedge lessthanb(B_i) \wedge IndSet(L_{i}) \wedge IndSet(R_{i})$
$Seq_{n} = empty(L_{n-1})$
So if we can prove that if there is a solution then there is a solution of maximum n rounds which is dependent on the size of the graph then I think we have a solution.
empty(X) = $\forall x \neg(x\in X)$
lessthanb(X) = $\exists x_{1} ... \exists x_{b} (\wedge_{i \neq j}\neg(x_{i} = x_{j})) \forall x (x \in X) \rightarrow (x=x_{1} \vee... \vee x=x_{b})$
IndSet(X) = $\forall x,y \in X \neg(R(x,y))$
