It’s strange the things you notice when you’re reading a comic. Take this panel from DC Retroactive 1970s Batman:

“Oh, Willlllmmmaaaa!” 

I don’t know if this was intended by writer Len Wein and artist Tom Mandrake or if colorist Wes Hartman is just having a bit of fun. Of course, The Flintstones is part of the Warner Bros. animation empire, just as the DC Universe is.

It reminds me of this panel from X-Men #130, about which artist John Byrne later said he had hoped colorist Glynis Wein would pick up on his idea and color it in green, white and red. Here’s the printed panel:

The joke’s on Scott and Jean.

Oddly, Byrne also has said in interviews that he realized as a child that he could write stories with the best of them when he came up with an idea for a TV series about cavemen who had prehistoric equivalents of modern conveniences long before The Flintstones came on the air with much the same idea. 
I admit I liked the three Retroactive issues DC publicity was kind enough to send me, though I admit to not being interested enough to buy any more of them. This is a good idea for a project, and the reprints were nicely chosen, but it should have been spread out over more than a month. Six specials each for the 1970s, 1980s and 1990s at $4.99 a piece ads up to a whopping $89.82, which is way too much.