To add or not to add Manure to red leafed plants

Is it my imagination but did I read that you shouldnt add well-rotted manure to the planting hole of red and brown leafed plants as they will loose the colour i.e go green?
Currently planting a bog garden and have a rheum (ornamental rhubarb) Rodgersia and Darmera which all have coloured leaves. Thinking that the high nitrogen content may make the leaves green............what advise would you give? Love some photos of anyone else's bog/ damp garden and shady garden.
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for the fag ends of the aristocracy.