"Your colour spray lights up the crypt for a moment. You've caught the horror cleanly in its fan… but it continues to advance as if the spray of blinding light didn't exist."

Players are there to experience a world and events, with their characters in the middle of it, solving problems by their wits and kicking tail with their characters' abilities. Describing that world in a way that they can engage with it directly, instead of abstractly via the rules, is vital for many groups to maintaining the roleplaying part of "roleplaying game". The suggested narration above, or something like it, helps your players stay in the head-space of your imaginary world. Players should not be told why something unusual happened, by default—there's not much fantasy and wonder in exploring a fantasy world if everything fantastic is explained right away!

The player will already be puzzling at the discrepancy: "Why didn't that work? Is it resistant to other spells? There's no light in this crypt… does it not need its eyes to see? The chance of it being undead is pretty good if so…" For most people, this is fun! Don't interfere with that fun by immediately handing players the answer to every unknown they run into.

Of course, there are things that won't be unknown to the characters, things that naturally call for giving the players more information.

If the character does have special knowledge, such as Knowledge: Religion (which covers undead's abilities and weaknesses) or Knowledge: [local area] (which might give relevant rumours of the creature's behaviour), then ask for a check and follow up a success with the sort of information that would give them: "The colour spray failed to affect it, and you know that undead are immune to spells that confuse the mind…" or "You remember a story once about a young man who'd disturbed its lair being followed by the creature through a blinding, deafening storm as if the weather wasn't there."

The only time you should just tell (instead of show) your players why something is happening with no justification in the game world (like Knowledge skills, or reminding them of the last time they encountered a similar creature) is if it would directly interfere with what your group thinks is fun about the game.

Some groups play for the tactics and the efficient combat-plays. Further, some of those groups won't be interested in puzzling out the nature of fantastic things through the clues in your narration. If you're playing in this kind of group, by all means lay as much information on the table as you've got and move on with the fun parts of the game.

Throw Anything with a Tower Shield

At a guess, if you’re going with Throw Anything applied to a Tower Shield, you’re looking at probably 1d12 or 2d6, i.e. one of the larger, heavier weapons. The weight isn’t even close, but I don’t know that a Huge greataxe (3d6) or whatever is really a good match even though the weight is closest.

Heavy Shield

For Captain America, though, you really want to be able to use shield bashes. You’re much better off using a Heavy Shield (after all, his shield doesn’t look like a Tower Shield or impose the kind of difficulties that Tower Shields do). Heavy Shields can be used as a weapon with shield bash, and can be enhanced with magic as a weapon separate from their magic shield enhancements.

It can also benefit from shield spikes, which are definitely a good idea. Captain America’s shield doesn’t have spikes; I’d ask my DM to allow a “studded” or “reinforced” shield that deals the same damage but as Bludgeoning damage. If you cannot get that, the difference between 1d6 and 1d4 is only 1 damage on average, so that’s not too bad, but the difference gets quite a bit larger as you increase in size (and you want to do that, it’s one of the best ways to improve shield bash damage).

+1 Ranged Shield

But I wouldn’t use Throw Anything; a +1 ranged shield would deal 1d8+Str points of bludgeoning damage when thrown, and return to your hand by your next turn. This doesn’t require a feat at all, which is very good, and it’s a shield enhancement (i.e. cheaper than a weapon enhancement), which is better. However, it cannot be applied to a tower shield. A +1 ranged heavy steel shield costs 4,170 gp.

The problem with ranged is that the 1d8+Str damage is fixed, and it’s very difficult to improve it. Things like shield spikes, weapon enhancements, or becoming Large or larger don’t work. It does count as a ranged weapon, so you can get some bonuses to it, but most shield-specific feats aren’t going to work.

+1 Throwing Returning Shield

At a +3 equivalent, a +1 throwing returning heavy spiked shield deals 1d6+Str+1 damage by default (equivalent, on average, to the +1 ranged shield), but you can add a lot more bonuses to this because size and weapon enhancements matter. The +1 throwing returning heavy spiked shield costs 18,330 gp though: that’s way too much for what you’re getting. It is a lot better than the ranged shield, but you don’t need to spend all that gold on it.

Instead, there are the Gloves of Taarnahm the Vigilant from Player’s Guide to Faerûn, which add throwing and returning to any weapon you have. They’re 10,000 gp, but the shield could be a +1 heavy spiked shield (2,330 gp), so your total (12,330 gp) is still massively less than the +1 throwing returning heavy spiked shield. The savings only improve from there if you add more weapon properties, which you should since if you have none the ranged shield is probably better.

Bloodstorm Blade

A completely different alternative (but a popular one for Captain America, and a good choice in any event) is the Bloodstorm Blade from Tome of Battle. Among other things, it lets you apply throwing and returning to any weapon you like, without having to pay for it. It also has an ability to treat ranged attacks as melee attacks, which can mean very good things for the bonuses that you get to apply to them. Plus, it’s a Tome of Battle class, which means you have martial maneuvers. That makes you more versatile, skilled, and flexible than other martial classes (which are generally underpowered), which is generally a good thing.