In the latest release, SVG radial gradients appear to apply colour stops as solid black. Removing the <stop> elements produces a solid colour, but without a radial gradient.
Hans may be aware of the issue. Meanwhile, here's an MWE.
Save as gradient.svg:
<!-- SOF -->
<svg xmlns="
http://www.w3.org/2000/svg" viewBox="0 0 215.9 279.4" height="1056" width="816"><defs><radialGradient r="153.278" fy="276.602" fx="101.83" cy="276.602" cx="101.83" gradientTransform="matrix(0.41308681,-4.1069042e-8,4.7549103e-8,0.47826553,59.765073,10.270449)" id="A" gradientUnits="userSpaceOnUse"><stop offset="0" stop-color="#f9f9f9" stop-opacity="0"/><stop offset="1" stop-color="#4c1300" stop-opacity=".26"/></radialGradient></defs><g fill-rule="evenodd"><path d="M.127.127h215.646v279.146H.127z" fill="#f8da95"/><path d="M10.54 38.525h182.579v208.07H10.54z" fill="url(#A)" opacity=".75"/></g></svg>
<!-- EOF -->
Save as gradient.tex:
% SOF
\starttext
\placefigure{}{\externalfigure[gradient.svg][conversion=mp]}
\stoptext
% EOF
Expected: A light-brown, translucent, radial gradient region appears on the page.
Actual: A solid, opaque, black region appears on the page.
Environment:
Xubuntu Linux 5.8.0-48 (clean install on VirtualBox)
ConTeXt version 2021.03.27 19:09
Cheers!