See this link for a the problem and cure
Somehow, my guess is that your nook color has had some internal B&N files replaced with Clockwork Recovery files and this is preventing the update. When doing a stock update from one B&N software version to another, android guys, penguins and triangles with exclamation marks are a sign that you've got some work ahead of you.
This failure will occur whether you sideload the new B&N update or wait for an over-the-air update. To get the new B&N update, you need to replace the Clockwork files with the expected B&N files.