Hi Saurabh,
Thanks for using Syncfusion products.
I am afraid that i am not able to reproduce the issue that you have mentioned here.
Please refer the sample from the below link, which illustrates this:
http://websamples.syncfusion.com/samples/Grid.Web/6.4.0.15/Grid_Web_BackColor/main.htmWith latest version, we need to set "Handled" property to true, to apply the styles through QueryCellStyleInfo.
Please try this and let me know if this helps you out.
Regards,
Raji