Susan,
Try this:
1 - Select image with eyes you want to change
2 - Open Adjustments Inspector and place a check mark in the 'Color' brick
3 - Click the Color brick Action menu (cog wheel icon) and select 'Brush Color In'
4 - Set the brush size to the size of the iris of one eye and then click once over the eye to set a brush mark
5 - Click the eyedropper tool in the Color brick and click inside the iris (this samples the current color of the iris)
6 - Now use the 'Hue' slider in the Color brick to change the hue of the iris
7 - Repeat for other eye (or do both at once)
Note - you may have to play around with the sliders in brick to get the color you are looking for, but it should be workable if the original iris has color at all (you may notice that black and white are not affected by hue change). 😉
The other option is of course going to PS > creating a selection around the iris > bringing up a 'Hue/Saturation' adjustment > adjusting as needed. The Aperture method is much faster and can be removed quickly. 🙂