British Railway’s shades were all from the BS381 series; color patches can be found at these sites:
(Thanks to Andrew Emmerson & John Shelley for these).
The references to these colors can cause confusion, as they were prone to variation, darkened with age & weathering, and are often not precisely defined. Clearly, real stone can vary from the red of Devon & Ayrshire to the grey of the Peak District, but to a painter, ‘stone’ is a pale buff color, and that is the shade being referred to here by the use of the word ‘stone’.
All these paints were made by mixing the pigment with a white lead base. For the purposes of this web site, ‘Stone’ is very pale buff with a little yellow in the shade; ‘Cream’ is a similar shade containing more yellow, and ‘Buff’ is a darker shade which can approach a brown at times. If the railway company itself used the term ‘Stone’, however, I will also use it; the GWR & the SR used the term for colors that do not meet the above definition.