The amazing Shane Stanley saved me with the tip of a delay before the send step. My script was failing to send with attachments.
Shane thought it might be get have something to do with the animation added to creating/sending an email.
Try a delay after creating but before formatting? But hacky, but worked for me.
Sent from my iPhone
tell application "Mail"
activate
set p to 4
set newMessage to make new outgoing message with properties {visible:true, subject:the_subject, content:the_content}
set p to 5
do shell script ("sleep 2")
tell content of newMessage
do shell script ("sleep 2")
try
set y to count of the_content
set color of characters 1 thru y to textcolor
end try
try
set x to offset of my theBusinessName in the_content
set font of characters x thru (x + (count of my theBusinessName) - 1) to "Helvetica Bold"
set color of characters x thru (x + (count of my theBusinessName) - 1) to {56342, 2442, 607}
end try