colour change in row & column heads like row - 1,2,3.. & columns A,B,C..
In below image look at the row & column header ie "D" column and row "5" [not the cell] which background got highlighted with grey shade, that i want to change it to different colour. As understood it was available in previous versions of excel, but in MS Office 365 [excel] not available.

The grey color is part of the application color scheme. I don't recall being able to change that in earlier versions of Office.
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You can change it in Windows, by picking a different "Windows Theme". In earlier versions of Windows, that was something we could do, change individual settings. But that is one of many Windows user control settings / features that MS has (dis)"improved" out of recent versions of Windows. In the past we could also create custom "Windows themes". I don't know if that is still possible.
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There are some DIY fixes for this problem
Highlight the Active Cell, Row, or Column
https://docs.microsoft.com/en-us/office/vba/excel/concepts/cells-and-ranges/highlight-the-active-cell-row-or-column
09/13/2021
The following code examples show ways to highlight the active cell or the rows and columns that contain the active cell. These examples use the SelectionChange event of the Worksheet object.
Excel tricks to highlight selected row, column, heading and more
https://office-watch.com/2019/excel-tricks-to-highlight-selected-row-column-heading-and-more/
3 December 2019
You can make it easier to see your current place in a workbook by dynamically highlighting the selected row, column, cell or headings. Here’s obvious and more subtle highlighting options plus the downside of highlighting, real world tips and
debugging tricks if you’re having trouble.
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How to auto-highlight row and column of active cell in Excel?
https://www.extendoffice.com/documents/excel/1494-excel-highlight-active-row-and-column.html
When you view a large worksheet with numerous data, you may want to highlight the selected cell’ row and column so that you can easily and intuitively read the data to avoid misreading them. Here, I can introduce you some interesting tricks to highlight the row and column of the current cell, when the cell is changed, the column and row of the new cell are highlighted automatically as following screenshots:
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How to highlight active row and column in Excel
https://www.ablebits.com/office-addins-blog/highlight-active-row-column-excel/
by Svetlana Cheusheva | updated on December 28, 2021
In this tutorial, you will learn 3 different ways to dynamically highlight the row and column of a selected cell in Excel.
When viewing a large worksheet for a long time, you may eventually lose track of where your cursor is and which data you are looking at. To know exactly where you are at any moment, get Excel to automatically highlight the active row and column for you! Naturally, the highlighting should be dynamic and change every time you select another cell. Essentially, this is what we are aiming to achieve: