Here you can see two Hoya carnosa leaves.

Reasons for this difference: The Sun

Whit the sun: is smaller, more fleshy and lime green

Without the sun: is bigger, thinner and greener.

If it has dark green is probable that it will not flourish in a long time

the same for Krimson queen.

You can see hojas carnosas "diferencias"

Here is a link that might be useful: hojas carnosas