Google periodically tests different colored stars in their search results.  While we have seen variations of yellow and orange, Google has also tested teal, green and red colored stars as well.  And now they are testing blue stars.

Ramesh Singh shared this screenshot of bright blue stars.  The screenshot shows recipes with the blue review stars, but they are also showing for the other review stars as well, including local results.

Here is an example of ratings and the local knowledge panel.

Google has a history of testing out a variety of colored stars in their search results, and seem to be going through a testing phase currently.  We also spotted them with teal stars last week.

These seem to be just a 1% test, as the colored stars seem to be showing on a limited basis right now.