I doubt that. I always thought that X signifies luminance and Y intensity. I looked it up just now to be sure. This from RawPedia:
The curve has the additional advantage of letting you control noise reduction strength as a function of the pixels’ luminance - e.g. it allows you to have strong luminance noise reduction in the shadows and none in the highlights.
If you want to tackle noise in a specific colour range you might want to have a look at the Local Adjusments tab, which can do this.
Set one or more spots (using spot method - Full Image) based on colour and attack the noise using the Blur/Grain & Denoise tool.
EDIT: @Andy_Astbury1 did a video about how to approach this:
If you want/need an example to play with, I tried out this method in this edit: