Set colors of GO terms.

def _init_goid2color(self):
        """Set colors of GO terms."""
        goid2color = {}
        # 1. colors based on p-value override colors based on source GO
        if self.go2res is not None:
            alpha2col = self.pltvars.alpha2col
            pval_name = self.pval_name
            for goid, res in self.go2res.items():
                pval = getattr(res, pval_name, None)
                if pval is not None:
                    for alpha, color in alpha2col.items():
                        if pval <= alpha and res.study_count != 0:
                            if goid not in goid2color:
                                goid2color[goid] = color
        # 2. GO source color
        color = self.pltvars.key2col['go_sources']
        for goid in self.godag.go_sources:
            if goid not in goid2color:
                goid2color[goid] = color
        # 3. Level-01 GO color
        color = self.pltvars.key2col['level_01']
        for goid, goobj in self.godag.go2obj.items():
            if goobj.level == 1:
                if goid not in goid2color:
                    goid2color[goid] = color
        return goid2color