For this exercise I used a black linen mix fabric and a variety of knitting yarns and embroidery threads in yellow and red.
I tried stitching a variety of samples. The first was lines of chain stitch alternating in red pearle and yellow embroidery thread, starting with a thick line made up of several rows of one colour and then thinner lines using one row of stitching. I find that the red colour recedes on this black fabric and the yellow is very prominent. Where the rows of chain stitch get thinner the red seems to retreat even further.
In the next sample, I used chunky acrylic knitting yarn and couched it on to the background fabric using standard machine sewing thread. This gives a large expanse of yellow with dashes of red. At a distance the whole disc seems to become a slightly more orangey yellow and you don’t really see the red threads.
In this sample using cotton threads I have made an area of solid backstitch which opens up to show more of the background black. I have done the same with the red in a curved shape which means there are solid blocks of colour to start with which then grade into more open stripes. Where the yellow is solid against the black it appears more vibrant and then where you see more of the black ground through the colour is toned down and recedes slightly. The same happens with the red threads but here you also see the yellow threads, along with the black behind and this mixes the red and yellow a bit more.
Here I have used cotton threads in a slightly darker red with the yellow, beginning with a more concentrated area of fly stitch on the right which opens up a little towards the left showing more black fabric. Where there are more areas of black showing the red appears darker and where the yellow stitches touch the red they seem to brighten it.
In the sample below I used some red ribbons along with the embroidery threads to give areas of solid colour to base the yellow stitches on. I have used couching over some more chunky knitting yarns, cross stitch, running stitches and french knots. Where I have cross stitched over the transparent red ribbon the stitches appear toned down because they are quite spaced apart and, I think because the background black shows through the red ribbon. Contrast this with the French knots on the same ribbon. Where the knots are close together the effect is bright and where they are less frequent towards the bottom the yellow is less bold. Also, where the yellow running stitch has been placed over a red ribbon, although it is spaced out the yellow appears more vibrant than where I have done a couple of lines of running stitch directly onto the black background to the left. Here the yellow stitches recede, even though they are slightly closer together.