You're right about the colours, but it wasn't intentional. This is a bug from the latest release of mempool.space and the official instance fixed it. We could fix it too, but it does fit quite well, because most nodes and miners won't accept <1sat/vB txs, so they are a bit risky to rely on.
I understand, and it's not a big deal, but red/green color is showing how full or empty blocks are, not how risky something is 
And if transaction is sent with RBF than fees can be updated later.
That said, we made sure our node is connected to other <1sat/vB nodes, so if you want to broadcast such a tx you can do so here: https://mempool.orangefren.com/tx/push and it ought to reach the miners that accept such txs.
Very nice! I am bookmarking this one.I still can't get used to sending coins with such low transaction fees, but this tool can be very useful.