There is a lot of variation. Are the temps cooler? Sometimes melanization across the caterpillar is because of cooler temperatures. If the caterpillar has OE, it tends to be more sluggish and have very dry frass. The caterpillars almost seem constipated.
-Elisabeth

Here are some Monarch cats that I took a picture of two years ago. You can see how they can vary in color. I've had some a few times that had next to no black in them at all, just yellow and white mostly. I wish I'd have had one of those at the time that I took this picture; I'd have put it in the picture too.

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This website has a picture of a caterpillar that actually has Oe.

Here is a link that might be useful: OE Spores

I was looking around on the computer to see if I had one that was more yellow and found one. Now you'll just have to imagine this one beside my other three above. :)
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Yes, my house is air conditioned so temps are definitely cooler than outside. I didn't realize that can make a difference! Interesting!

Caterwallin, so all those cats eclosed successfully and were healthy? That makes me feel much better!

Thanks all!

If they appear healthy, then they probably are. You can test them after they emerge. Some that have the OE will not make it out of their pupa. Others, will emerge and appear healthy. Learning to test them will let you know if they really have the spores. But, there are other things that can cause disease; for example, bacteria.

I've listed the Project Monarch Health website, it has information about how to raise healthy Monarchs and how to test for OE.

Here is a link that might be useful: Project Monarch Health

Some years ago I came across research done in Canada, with regard to monarch development and ambient temperature. They found out that when the temperature of the environment is around 81 degrees F, the caterpillars and chrysalids develop to maturity in the shortest time. Wide black stripes on monarch cats are a sign of cool temps. If the caterpillar is infected with Oe, the chrysalid might have dark patches.

Temperature constraits for Monarchs:
31 C to 35.5 C temperatures become lethal (87.8 to 95.5 F)
12 C development threshold (53.6 F)

The Monarchs have ways of controlling their temperature. Staying under leaves during the day when it is hot. In the late fall, I've seen Monarchs and Black Swallowtails caterpillars get darker. They do absorb more light and can warm up faster.

Here is a link that might be useful: Temperature Constraints

sitali301, Yes, I'm happy to say that those in the pictures all eclosed successfully. I've had Monarchs (and other kinds) that didn't eclose successfully, but that's to be expected. Of the ones that I raise, though, far more make it than don't make it. Best of luck with yours.
Cathy