highlight an instance where a volume reported is unchanged from the previous month
Highlighting would most likely be done in a client tool like Reporting Services. From a TSQL point, you could add an additional column to your result to signify 'No change'.  If you're on at least SQL Server 2012, you can use LAG.

--Setup demo data
declare @t table (Fields varchar(30), Name varchar(30), [Month] varchar(10), Amount int)
insert into @t(Fields,name, [Month],Amount) values
('Instance1','Alan', 'Jan2018', 120),
('Instance2','Alan', 'Feb2018', 140),
('Instance3','Alan', 'Mar2018', 140),
('Instance4','John', 'Jan2018', 50),
('Instance5','John', 'Feb2018', 50),
('Instance6','John', 'Mar2018', 60)

--The actual query
--Using a Common Table Expression, create a SortOrder column
;
With _cte as
(
SELECT *
    ,SUBSTRING([month], 4, 4) + CASE 
        WHEN substring([month], 1, 3) = 'Jan'
            THEN '01'
        WHEN substring([month], 1, 3) = 'Feb'
            THEN '02'
        WHEN substring([month], 1, 3) = 'Mar'
            THEN '03'
        WHEN substring([month], 1, 3) = 'Apr'
            THEN '04'
        WHEN substring([month], 1, 3) = 'May'
            THEN '05'
        WHEN substring([month], 1, 3) = 'Jun'
            THEN '06'
        WHEN substring([month], 1, 3) = 'Jul'
            THEN '07'
        WHEN substring([month], 1, 3) = 'Aug'
            THEN '08'
        WHEN substring([month], 1, 3) = 'Sep'
            THEN '09'
        WHEN substring([month], 1, 3) = 'Oct'
            THEN '10'
        WHEN substring([month], 1, 3) = 'Nov'
            THEN '11'
        WHEN substring([month], 1, 3) = 'Dec'
            THEN '12'
        END AS SortOrder
FROM @t)

SELECT *
    ,CASE 
        WHEN LAG(amount) OVER (
                ORDER BY NAME
                    ,SortOrder
                ) = amount
            THEN '**'
        ELSE ' '
        END AS NoChangeFromPreviousMonth
FROM _cte
order by name,SortOrder




| Fields    | Name | Month   | Amount | SortOrder | NoChangeFromPreviousMonth |
|-----------|------|---------|--------|-----------|---------------------------|
| Instance1 | Alan | Jan2018 | 120    | 201801    |                           |
| Instance2 | Alan | Feb2018 | 140    | 201802    |                           |
| Instance3 | Alan | Mar2018 | 140    | 201803    | **                        |
| Instance4 | John | Jan2018 | 50     | 201801    |                           |
| Instance5 | John | Feb2018 | 50     | 201802    | **                        |
| Instance6 | John | Mar2018 | 60     | 201803    |                           |