              .attr("cy", (d) -> chrYScale[data.probes[d.probe].chr](data.probes[d.probe].pos_cM))
              .attr("r", peakRad)
              .attr("stroke", "none")
-             .attr("fill", "darkslateblue")
+             .attr("fill", (d) ->
+                 if (chrindex[d.chr] + chrindex[data.probes[d.probe].chr]) % 2 == 0
+                   return darkblue
+                 else
+                   return darkgreen)
              .attr("opacity", (d) -> Zscale(d.lod))
              .on "mouseover", (d) ->
                  d3.select(this).attr("r", bigRad)
                                 .attr("fill", pink)
-                                .attr("stroke", "darkslateblue")
+                                .attr("stroke", darkblue)
                                 .attr("stroke-width", 1)
                                 .attr("opacity", 1)
                  eqtltip.call(this,d)
              .on "mouseout", (d) ->
                  d3.select(this).attr("r", peakRad)
-                                .attr("fill", "darkslateblue")
+                                .attr("fill", (d) ->
+                                    if (chrindex[d.chr] + chrindex[data.probes[d.probe].chr]) % 2 == 0
+                                      return darkblue
+                                    else
+                                      return darkgreen)
                                 .attr("stroke", "none")
                                 .attr("opacity", (d) -> Zscale(d.lod))
                  d3.selectAll("#eqtltip").remove()

            .datum(data.pmarknames[c])
            .attr("d", lodcurve(c))
            .attr("class", "thickline")
            .attr("stroke", "darkslateblue")
            .style("pointer-events", "none")

    # title

       .attr("cy", top[1])
       .attr("r", bigRad)
       .attr("fill", pink)
       .attr("stroke", darkblue)
       .attr("stroke-width", 1)
       .attr("opacity", 1)

  chrindex = {}
  for c,i in data.chrnames
    chrindex[c] = i

  # circles at eQTL peaks
  peaks = svg.append("g").attr("id", "peaks")
