Nice solution.
I have an extension -- I've added a preflight profile that eliminates the need for the Resize node. The attached profile uses Gamma 1.8 on the odd pages. See Callas PDF ToolBox screen snaps.
The attached Workflow will convert odd pages to Grayscale. It will convert all objects to Grayscale using a “Dot gain 15%” ICC profile.
The workflow uses three components. FIrst it “tags” the odd pages. For this I have used the Resize component and set the Art box to 10 by 10 mm on the odd pages only. Second component is a Preflight which converts all objects to Grayscale on pages where the Art box is exactly 10 by 10 mm. Lastly the Art box is removed.
Import the workflow file “Convert_Odd_Pages_To_Grayscale.ffc” using the “Core Exchange”.
The Preflight profiles is made with PDF Tool Box but could also be created with Acrobat Pro. Theese two images show the settings if you want to use other profile settings. 
This workflow is kind of a workaround to get what you want. I think it would be a good feature request if we could get Page selections for the “Manage Color” component. Then we could do this kind of changes using on one Component.
