Final answer:
The provided information pertains to an art installation and does not include sales data for store A and store B, so an answer cannot be given based on the given context.
Step-by-step explanation:
The question does not provide sufficient data regarding the sales of umbrellas by store A and store B in the given months. The provided information discusses an art installation project involving blue and yellow umbrellas installed in Japan and California, respectively, not the sales data of two stores. Without specific sales numbers for the months mentioned, it's impossible to accurately answer which month store B sold more umbrellas than store A.