I was thinking of sleeving each of the player card decks in their respective colors (i.e., Tactics in red, Lore in green, etc.). If I were to enter a tournament with a Spirit/Tactics deck sleeved in this manner, would it be legal to play, and if so/not, why?

This game is cooperative, so there are no tournaments. The only “organized play” is very friendly and casual, so go ahead!

It would give you some information you're not supposed to have, so some people might not appreciate it. The most problematic case is that you're likely to have few neutral cards in your deck, so if you're sleeved them a particular way you'll know where they are.

24 minutes ago, NathanH said:

It would give you some information you're not supposed to have, so some people might not appreciate it. The most problematic case is that you're likely to have few neutral cards in your deck, so if you're sleeved them a particular way you'll know where they are.

That's a good point, I hadn't thought of that. However it seems to me that since it is a cooperative game, it wouldn't be that big a problem. What is your personal opinion on the matter?

Personally I think it would take away some of the fun of playing the game, and if I were to play cooperatively I wouldn't like it if someone did that.

You're not supposed to know what's coming next unless you use a card effect to look at the deck, but even with just different coloured sleeves you would know that the next card is a Tactics card, so you can plan your resources in advance.

It would also affect shuffling. When you shuffle the deck you're supposed to randomise the card draw, but you could easily shuffle so that "Oh, surprise, I've managed to put most of the Tactics cards near the top, and I just happen to have a load of Tactics resources".

While it's certainly your choice, my opinion is that... there are official ways to make the game easier.

16 minutes ago, icabod said:

You're  not supposed to know what's coming next unless you use a card effect to look at the deck, but even with just different coloured sleeves you would know that the next card is a Tactics c  ard, so you can plan your resources in advance.  

I think this in particular is a big deal. Sure, there may be corner cases with riddles and such where knowing a little about your top card helps… But planning how to spend your precious resources is a fundamental part of the game, and knowing the sphere you're going to get next changes that calculus markedly.

Okay, so far I'm hearing a lot of good reasons for not sleeving my decks in their respective colors. In particular, this comment made a lot of sense:

2 hours ago, icabod said:

You're not supposed to know what's coming next unless you use a card effect to look at the deck, but even with just different coloured sleeves you would know that the next card is a Tactics card, so you can plan your resources in advance.

It would also affect shuffling. When you shuffle the deck you're supposed to randomise the card draw, but you could easily shuffle so that "Oh, surprise, I've managed to put most of the Tactics cards near the top, and I just happen to have a load of Tactics resources".

I hadn't thought about the fact that it does affect how you play the game if you know what's coming. It would actually spoil the surprise. Nice catch.