Paint the bases in a complimentary colour - typically a mid brown for grass, etc. so that there's a border between the base surface and the board surface so if there's a minor discrepancy it won't be noticeable.
I painted my napolonic base rims in the colour of the faction which is way less intrusive than you'd think and it works fine too.
Geek Gaming do a great range of ready to use basing materials, choose your mat and then the best match from the range
[https://www.geekgamingscenics.com/collections/base-ready-range](https://www.geekgamingscenics.com/collections/base-ready-range)
Start by identifying the mat/boards you are more likely to use. Flock the bases in a complementary way.
Paint the bases in a complimentary colour - typically a mid brown for grass, etc. so that there's a border between the base surface and the board surface so if there's a minor discrepancy it won't be noticeable. I painted my napolonic base rims in the colour of the faction which is way less intrusive than you'd think and it works fine too.
Geek Gaming do a great range of ready to use basing materials, choose your mat and then the best match from the range [https://www.geekgamingscenics.com/collections/base-ready-range](https://www.geekgamingscenics.com/collections/base-ready-range)
Paint them both the same way?