First, a quick oneliner for fun:

perl -pe 'chomp if s/^START//..s/^END//; s/\S\K$/ /' input.txt
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However, so far you haven't gotten an answer that sorts your fields the way you showed in your desired output, so I'll try my hand at that:

use warnings;
use strict;

my @ORDER = qw/ TIME ALT TEMP COLOR STRENGTH /;
my %ORDER = map {$ORDER[$_]=>$_+1} 0..$#ORDER;

local $/ = "\nEND\n";
while (<>) {
    s/\A.*^START\n(.*)^END\n/$1/ms;
    next unless /\S/;
    my @lines = grep {/\S/} split /\n/;
    @lines = map { $$_[0] }
        sort {
            return $$a[1] <=> $$b[1] if $$a[1] && $$b[1];
            return -1 if $$a[1];
            return 1 if $$b[1];
            return $$a[2] cmp $$b[2] }
        map { /^(\w+):/ ? [$_,$ORDER{$1},$1]
            : [$_,0,$_] } @lines;
    print join(" ", @lines), "\n";
}
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See Schwartzian transform and How do I sort an array by (anything)? for the sorting technique I used.