Rubio makes a product that give wood floors that grey look. Check them out online.

Filling gaps between timber floor boards can lead to disaster and is best avoided. Sanded and polished timber floors tend to swell slightly during the humid months of the year and shrink again in the drier months. This creates movement in the timber floor. If you fill the floor when the gaps are at their widest and then encounter some humid weather, the floors will swell, closing the gap and forcing the filling out of the grooves and cracking the timber floor finish. This looks far worse than gaps in the polished timber floors. If you can't live with the gaps, laying a engineered timber floor over the top may be your best choice. Painting your floors white is also best to avoid as this only accentuates the size of the gaps. Good luck with your decision. Engineered timber floors

I think a light colour which will brighten up your room. Blackbutt perhaps? We have Blackbutt in our house and a manufactured oak in our holiday house. Both are light any really lift the room.

Thank you. The finishes meet in the doorway in the picture as well as at the top of the stairs which is where the Lifeproof is installed.