Help hiding formula while a cell is not filled in, and auto colouring

[mmace]

I've made a weight loss spreadsheet for my wife and I'm needing help one one bit of it (total weight lost so far)

I have a column that I want to put in "total weight lost so far" so I currently have:
=sum(200-E3)
which is her starting weight (200) minus her current weight (E3)

this works fine, but for the rows where there's no weight yet it displays 200 (because it's 200-0), is there a way to leave it either blank, display "n/a" or display zero but be automatically filled in when something in column 3 is entered?

also, is there a way to make either text or a cell a certain colour if it meets certain criteria?
for example, if total weight loss is 14lbs then it changes colour, 28lbs a different colour etc (even if it means all numbers between 14 and 27 are that colour), this would be the same column as above
for those not in the UK 14lbs equals a stone which is what we use for weight here rather than just pounds


any help with this would be appreciated, thanks

Excel 2007, Windows Vista 32 bit ultimate

 

[onlyadrafter]

Hello,

try

=if(F3=0,0,200-F3) to not show 200.

look into CONDITIONAL FORMATTING for the colouring

 

[mmace]

brilliant, thank you v much