What do you mean by the 'bold' text's color? If you want to have both bold and colored text, you simply have to select bold, then go and select a color from the SCE Editor.
Good question. You should actually be able to set a default color for any bold texts. You just need to select the element that changes the font-weight of the text which is usually <strong>.
Try adding the following rule to your stylesheet.
Code:
.postbody strong { color:#39C; }
If you want this to affect all bold font globally, use this rule instead :