You can easily convert colour photos to a grayscale in the Develop module, either by:

  1. Pressing the V
  2. Clicking on the Grayscale of the right panel

Lightroom will do a pretty good job of converting but… There’s always a but, the pretty good job is not always the right job. In the right panel underneath the Grayscale it shows various colours and each one affect different portions of the photo.

Lightroom: grayscale mix

Lightroom: Gray Scale Mix

Colour Effect
Red Hide skin blemishes & change greeneries
Orange Change the skin tones
Yellow Minor changes to skin tones
Green Strong effect on plants and greeneries
Acqua Skies & water
Blue Skies & water
Purple Outdoor settings
Magenta Outdoor settings

These are just rough guidelines. They are good starting point and you will need to experiment with the channels.

Don’t forget to also adjust:

  • Contrast
  • Tone Curve

AFTER the grayscale conversion.