Why doesn't he try to ask people about all blue, or look for it, he can ask robin about all blue history or ask her if she could find all blue references in poneglyphs, but he didn't even mention it post-time skip,
if i remember correctly the last time he mentioned all blue was when he saw mermaids in fishman island
if i remember correctly the last time he mentioned all blue was when he saw mermaids in fishman island