Justpottering there are some gorgeous books about by Liz Hubbard (sadly she passed away far too early age 46 in November 1990) on free motion embroidery - a hardback book called Thread Painting published by David and Charles, my copy has the most beautiful scarlet poppies mixed in with wheat on the cover - it looks stunning, then there is a smaller paperback booklet called Gutermann Thread Painting and this one is published by Search Press. Both books have used Gutermann threads, and at the time of publishing Gutermann used to offer their thread reels in special packs of threads so Poppies a range of reds through to oranges, Marigolds were yellows and light oranges, Greenwood were greens and of course there were other pack colourways as well. Each reel in the pack was only 50mtrs and there were 10 reels to each pack. Liz also used some paints to colour wash fabric before stitching, so say a sky, and then she would embroider a landscape picture using mostly zigzag stitch and the results absolutely stunning. She also has sewn cottages, gardens, river scenes - all are so pretty. Liz used to go into schools where she lived and got children to design their own pictures and stitch them out.
Another author of free motion embroidery is Alison Holt and her book is called Machine Embroidered Landscapes published by Batsford.
Have a look on abebooks UK website, or perhaps Amazon market place for these books. By the way you do not have to have a super fancy machine to be able to do this, Liz's machine was a Bernina Matic 803 so think back to around 1970's for this machine - the hard back book was published 1988. There is a good section at the front of the book showing you how to go about using your machine to create free machine embroidery so that is helpful.
Hope this is helpful to you for whatever you are trying to achieve with this type of embroidery - go and have fun.