OK. For all you shy Graminacea experts, here's the reason I asked the question.
I ventured in to a part of the garden where I very rarely go, the 'cow manure' heap area! This is solely the realm of Nora who watches the heaps, ensuring perfect rotting before using on our food ( plants ).
Out of the corner of my eye I noticed a 'dead' patch of grass close by. Upon investigation it turned out to be a very well variegated patch of what seemed to be the same as the other grass in this area
How do I check ( knowing little about grasses ) that it is as it seems and not an interloper delivered by seed by external agencies please?