Your chicken is fully cooked after simmering for an hour. The red bits are from the bone marrow and don't indicate that it's undercooked. You'll see the same thing if you roast a chicken, and you'll notice that the red bits are always in the meat surrounding bone joints.
Wilting in greens is triggered by temperature, pH, and salt content. To reduce wilting, you can cool the vegetables or shrimp, make the vegetables more acidic*, or decrease their salt content.
My suggestion would be to cool the shrimp with an ice water bath or cold running water. This is the most traditional approach for shrimp salad. Alternately, you could apply an acidic dressing before topping, but wait to salt it until the shrimp have cooled to 140F.
Alternately, wilting of vegetables adds a rather interesting variation in flavor or texture to a salad. This technique has been desirable and in vogue at various times.
Why does this all happen?
Plant cells wilt when cooking breaks apart the cellulose-based cell walls, and allows water to escape, causing them to soften. To quote On Food and Cooking (pp 282):
When the tissue reaches 140F/60C, the cell membranes are damaged, the
cells lose water and deflate, and the tissue as a whole goes from firm
and crisp to limp and flabby.
Acids will impede wilting, because the cell walls are held together with hemicellulose, and it is "not very soluble in an acid environment" (pp 282). Table salt is a problem, because "its sodium ions displace the calcium ions that cross-link and anchor the cement molecules in the fruits and vegetable walls, thus breaking the cross-links and helping dissolve the hemicelluloses" (pp 283). Calcium has the opposite affect, so if you can use hard water or add calcium salts, do so.
*Acidic solutions will reduce green colors(On Food and Cooking, pp 280-281), but preserve texture (282).
Best Answer
Marshmallows will dissolve ("melt") in your hot cocoa for the same reason that they "melt" in your mouth: both provide heat and moisture. If you could somehow treat the marshmallows so that they didn't dissolve in the cocoa you wouldn't get the desired effect in your mouth either. It comes down to a matter of timing: how can you keep the marshmallows intact until you drink the cocoa?
I can think of three options:
Drink the cocoa more quickly.
Use larger marshmallows.
Add more marshmallows as necessary.
It's not clear from your question exactly what kind of marshmallows you're referring to. I suspect that you're talking about the crunchily dehydrated "micro-mini" marshmallows that come in a packet of hot cocoa mix. Call me a snob, but those things hardly qualify as a "marshmallow" at all; you should perhaps be happy that they dissolve, or else sift them out of the mix and throw them away! If you like them, though, you'll be happy to know that you can buy more: Amazon carries 12 oz. bags of dehydrated micro-mini marshmallows, and adding a spoonful to your cup when you're ready to drink should solve the problem.
If you feel like an upgrading your brew, pick up a bag of mini marshmallows and add a handful of those. Minis should be large enough to last for quite a while, and since they're not dehydrated they'll be somewhat sturdier in the cup. Marshmallows come in a number of sizes... if the minis don't last long enough for you, go with a few standard sized (approximately 1 inch) marshmallows. I've seen jumbo marshmallows in the store lately, but you'll probably need a larger cup if you want to have any room left for the cocoa. Try one of these lovelies.