Can we splash a second color AND play Solitude?

Unfortunately, I don’t believe that we can afford to play both Solitude AND have the mana work with a splash color. You can definitely make it work, but if you want the requisite 11+ blue sources, you have to make some real concessions in how you build your mana; you effectively have to go up to 23 lands, cut all the canopy lands, and cut at least 1 Inkmoth. The Emeria’s Calls, coupled with the necessity of a fetch/shock manabase means that you WILL lose close games due to the amount of damage you do to yourself. For reference, I tried both a UW build and a WB build, and I lost to burn for the first time in a long time by 1-2 life points each time.

To expand on this with actual lists:

Lonely Hammer Mana (22 lands)

4 Saga

3 Inkmoth

4 Emeria’s Call

10 Plains

1 Canopy Land

Non-lonely UW Hammer manabase (22 lands)

4 Saga

3 Inkmoth

1 Canopy Land

3 Plains

2 Hallowed Fountain

3 Seachrome Coast

6 Fetchlands

You can see here we have 15 White sources in Lonely, and 15 White + 11 Blue Sources in UW. Here is what we would be looking at if we wanted to keep these color counts the same while still getting the Calls in there:

Lonely UW (22 lands)

4 Saga

3 Inkmoth

4 Emeria’s Call

2 Hallowed Fountain

3 Seachrome Coast

6 Fetchlands

Does this manabase technically work? Yes. Is it incredibly painful? Also yes. Also, it cannot beat a Blood Moon. So let’s try something a bit greedier, which still requires adding a land (23 lands)

4 Saga

2 Inkmoth

4 Emeria’s Call

2 Hallowed Fountain

2 Plains

3 Seachrome Coast

6 Fetchlands

If you really wanted to play Solitude AND splash, I think you would realistically have to do something like this (23 lands)

4 Saga

1 Inkmoth

4 Emeria’s Call

2 Hallowed Fountain

3 Plains

3 Seachrome Coast

6 Fetchlands

(22 lands)

4 Saga

4 Emeria’s Call

2 Hallowed Fountain

3 Plains

3 Seachrome Coast

6 Fetchlands

While this works, losing consistent access to Inkmoth kills is simply not worth the trade-off in my opinion.

Tl;dr: I don't believe it is optimal to splash a second color in a Solitude build.