if the <18 condition supposed to be based on a group or report SUM?

Your current formula is a row level analysis of the value of that field on that row.
If you want the sum to be highlighted use the below formula on the sum field.

if {TrainingObjectiveHistory.tohobjTitle} = "iso facility use hours" and SUM({TrainingObjectiveHistory.tohseshrs}) <18

Although I think you still have an issue because this would be the the total sum and not the sum where the row is like the "iso..." condition. If you are trying to that you need to use a conditional running total or another formula field that you would sum.

//iso_only formula
if {TrainingObjectiveHistory.tohobjTitle} = "iso facility use hours" then {TrainingObjectiveHistory.tohseshrs} else 0

sum that to see if it is <18
SUM(@iso_only)

so you want to change the font color of tohobjTitle field?
You want the field to be red when what the title value = 'iso facility use hours' and the sum of all tohseshrs < 18 or only if the sum of the tohseshrs rows where title = 'iso facility use hours' < 18?

Create a formula field you will use to get the sum where only title = 'iso facility use hours'
call it something like "iso_facility_use_hours_only".
it will be
if {TrainingObjectiveHistory.tohobjTitle} = "iso facility use hours" then {TrainingObjectiveHistory.tohseshrs} else 0
now you will sum that formula field
for the color condition it will be

if {TrainingObjectiveHistory.tohobjTitle} = "iso facility use hours" and sum(@iso_facility_use_hours_only)<18 then CrRed else CrBlack

Or you might consider grouping on tohobjTitle and using the group level sum but that will possibly change your sort order or structure too much for whatever else the report is for.

can you copy and paste the exact text you are using for that condition format