Yes, you can do that in the tickOptions
the textColor attribute defines the color of the tick along the axis
the tickOptions apply to.
axes: {
xaxis: {
renderer:$.jqplot.DateAxisRenderer,
min:'August 1, 2007',
tickInterval: '4 months',
tickOptions:{formatString:'%Y/%#m/%#d', textColor :
'#ffffff'}
},
yaxis: {
renderer: $.jqplot.LogAxisRenderer,
tickInterval:'50',
tickOptions:{formatString:'$%.2f', textColor : '#ffffff'}