For some - myself included - the idea of being "non-striving" is somewhat foreign!
I know that I enjoy colouring mandala's because they are relaxing, decrease anxiety and are a nice way to be in the moment and practice mindfulness. However, when colouring that mandala becomes: how to make it look better, needing to get it completed, being annoyed with colouring outside the lines....and even for me....wanting to make a giant collage with them......all these are....STRIVING!
A way I look at is perhaps not having a goal? Not needing to be perfect, and just doing something for the sake of doing it. Not focusing on what the end result will be or how that will make you feel. Try NOT finishing something. It's interesting to observe what feelings arise.
Although adult colouring books get flack, it really is an excellent way to stay present, in the moment and be mindful. Mandala's are great because you choose to either start from the inside and colour towards the outside or vise versa. In sanskrit, Mandala means circle. They are a symbol that represents the universe. In various spiritual traditions, mandalas can be used for focusing attention, as a spiritual guidance tool, for establishing a sacred space and as an aid to meditation (paraphrased from wikipedia).
Namaste