But What Decade is this Dress?

As this year comes to a close, I'm heading to a New Year's Party where the theme is "DECADES." Partygoers need to dress in any decade they choose. 

I'm a lucky girl - the host of the party sent me a dress to wear as well! I haven't seen her yet to ask anything about this dress, but she volunteers at a thrift shop, so perhaps it came from there.

Now, here's my question: What Decade is this Dress?

A small tag on the side seam tells me the dress was made in East Germany. Made of a knit fabric with the bold diagonal pattern printed on, the only fitted part is two simple tucks on the bodice. The colorful op-art design might place it in the 60s, but because it's so unstructured, I'm guessing the 70s. What do you think?

Loretta