Hi @KevinPlant,
I'd suggest you fill the hole in your door with Polyfilla Exterior Timber Filler. It can be used in external or internal applications, can be sanded, stained, painted or clear-coated depending on what you would like to do.
It is a greyish colour, so you would need to add a coating over the top both to protect it and help it blend in with the surrounding timber. Paint is the obvious choice to me, as you can use a combination of two colours to help blend it in with the natural wood grain of the door. Using a craft brush, you can layer the colours and emulate the grain pattern as closely as possible.
Unfortunately, as you wouldn't be able to remove a chip from the door to get a close paint match, the best solution that I can suggest is to head in store and grab a few different paint cards that appear close in terms of colour, then head home and compare them with the door. When you have selected your colours, head back in store, and the team at the Paint Desk will be able to help you mix them up.
Being that it is an external door, you would need to use an exterior paint such as Dulux Weathershield or British Paints 4 Seasons.
Alternatively, you could use an exterior stain, but you would not be able to emulate the grain pattern in the same way as you could with paint.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
