I changed low graphics / low fps / multisampling back and forth, then when loading a game with normal setting after having it saved with low graphic this happened
This is a debug visualisation to show water flow (pipes / boilers / steam engines / etc.). Not sure how it got switched on though. You can open the debug visualisation gui with F4 and make sure nothing is selected in the "always" tab.
I also enountered this on first gameplay in version 0.9.0. But I thought this might be result of Factorio importing old settings from version 0.8.8. So I haven't reported this isue.