Ideally, that would be aces and can be done, but there are reasons not to, i'm afraid. Due to the ZX Spectrum attributes - 2 colours per 8x8 pixels - then if any sprites overlap it can get a bit messy, though there are routines to make a sprite's colours the main overriding colours. It doesn't help that there is no masking in the sprites. As a rule, i always do masking, but again i've been asked not to bother due to restrictions, though, again, this can be calculated programmatically and again, unfortunately, out of my hands. So, yeah, it can be done - thinking off hand, Ultimate/Rare's Jetpac is a good example.
In the first game build, the customer faces graphics had lost the colour and were all black and yellow as the programmer wanted them to drop in and slide down the screen which meant having them in mono only for them to move...hopefully i talked him out of this.