Actually I didn't bother to get the masking tape out, but used an old and rarely mentioned technique - simply scoring the line on the fabric and this has worked very well on the white cotton that I am working on. I have then stitched this line with the clear thread and it shows up well enough for the purpose.
The advantage of using the clear thread is that you don't split it when sewing over it, which will make the frogging easier. And I would rather frog than wash this one.
Masking tape is great for straight line designs , unfortunately I will not be doing straight lines - the design is going to me more like this
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A contrasting colour is usually a good idea, but because it is a bright white if I were to use a different colour when I came to take the marking stitches out it would probably leave behind small fibres of the other colour and would never completely be removed and would shadow the fabric. (This can be a problem for those who make wedding dresses too).
All the ideas mentioned here are equally good, it just depends upon individual circumstances and preferences.