I've prepared a demo for min/max value conditional formatting.
This is done with JS code and only format what are on current page.

https://gist.github.com/gridphp/12895a38ff7681c4519fb461301bcadd
99,108-119,137-143

Fantastic Abu, really helpful to see the code. Can I ask what the 'ids' refers to ion this as I cannot make it work in any of my pages?

In my example below I have 12 columns, one for each month. I tried to test it on column name 'Jan' but that doesnt work?

<script>
function grid_onload(ids)
{
var low;
var low_index;
var high;
var high_index;

if(ids.rows)
jQuery.each(ids.rows,function(i)
{
// find lowest value
if (low == undefined || parseInt(this.Jan) < low)
{
low = parseInt(this.Jan);
low_index = i;
}

// find highest value
if (high == undefined || parseInt(this.Jan) > high)
{
high = parseInt(this.Jan);
high_index = i;
}
});

// highlight lowest client id
jQuery('#list1 tr.jqgrow:eq('+low_index+')').css('background-image','inherit');
jQuery('#list1 tr.jqgrow:eq('+low_index+') td[aria-describedby=list1_Jan]').css('background','inherit').css({'background-color':'#000', 'color':'white'});

// highlight highest client id
jQuery('#list1 tr.jqgrow:eq('+high_index+')').css('background-image','inherit');
jQuery('#list1 tr.jqgrow:eq('+high_index+') td[aria-describedby=list1_Jan]').css('background','inherit').css({'background-color':'red', 'color':'white'});
}
</script>

Hi Abu, please ignore my last post I figured it out, forgot to add the line $grid["loadComplete"] = "function(ids) { grid_onload(ids); }";

Apologies. Works great, if I want to use this on 12 columns would I need to recreate the script above for each column (1 per month, Jan, Feb, Mar etc etc etc

I think yes. You will need all those variables for low/high of each column.

Please note this only apply on current page, not on all records of database table.
For all db records, some server side code would be required.