Try the following:
if (Group == 'Customer') {
if(Status != 'Agreement') {
cell.css ('color', 'blue');
}
}
else if (Group == 'Non-customer') {
if (Staus == null) {
cell.css ('color', 'green');
}
else if (Status != 'Agreement') {
cell.css ('color', 'yellow');
}
else if (Status != 'Not declared') {
cell.css ('color', 'purple');
}
}
solved IF ELSE in Java Script