Coloured lines on a greyscale image

Are you asking about adding guides?
View>Rulers, then click and drag from the ruler.

Hi, was there a solution to your question? Just making sure you found your answer.

thank you,

Thanks everyone for your help 🙂

Technically one could also add Spot Channels to a Grayscale image but that would only approach making sense if one actually prints with Spot Colors … 

And depending on the output needs and the linework’s complexity it might make sense to create it in a vector ariented application like Illustrator or Indesign. 

Hi,

I could be a simple as this, switch from Grayscale to RGB Color, then your color layers will show as color.

You'll need to change your mode from greyscale to either RGB or CMYK depending on your needs. 

warmly/j

If you need the image to print in K only you could to copy the Channel, convert the image to CMYK, fill C, M and Y with white and paste the image into K. 

The add Shape Layers for the lines. 

You'll have to convert the Mode to color.