82 YZ250 Identifying rear spring

[bultaco4ever]

I just got an '82 YZ 250J and the rear shock needs to be rebuilt. The spring also seems way to soft for my, ahem, manly physique. The current spring on it is black in color. My manual says that black was the softest spring offered. Can I rely on that? There's a guy on fleabay offering the heaviest duty spring but his photo shows a black spring. I'm under the impression that the standard and heavy duty springs should be white.