This is a really nice horse: http://www.renderosity.com/mod/bcs/adhorse-a-new-horse-figure-for-poser/73561 although the closest the base texture set has to white is a very light grey.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3