Is it possible to split one private vlan (or isolated vlan) between two networks? so the "white" vlan from network 1 can only communicate with its peer in network 2?
There's no need to share a VLAN across those two sites - all addressing is unambiguous and a routed link will work nicely. It's a model case for a VPN tunnel.
I'd suggest setting up an IPsec tunnel. You'll also need a routing protocol like OSPF or static routes for the respective remote networks.
Connecting the networks with a shared VLAN would require a bridged/L2 tunnel which can be quite cumbersome over WAN.