This particular problem — which is not to be confused with similar-looking problems in later versions with .im8 images (such as the graphics on the 'Welcome to Solaris' splash screen) — is a known issue with Motif:
1255448: cde on Solaris x86 has yellow tinting problem with TrueColor default visual An X server that allows changing the class of the default visual should be able to work around this.
Xorg and Xming document an option for that:
-cc int default color visual class
However passing -cc with PseudoColor or its constant from X.h (3) has no effect on the default visual reported by xdpyinfo.
Alternately the issue can be fixed by installing a revision of the appropriate Motif patch for the Solaris release (e.g. 2.5 → 103947, 2.5.1 → 104195) that has a fix for this issue.